Right, I'd say the biggest thing that people overlook is the case, get a nice one, with machined edges. There's nothing so infuriating as trying to work in a small, poorly designed case, and cutting your knuckles on jagged, metal edges.

More expensive motherboards come with very detailed manuals that cover the details of each and every connector. They'll also label each connector with a code, so you can reference the manual on it if you need. One other thing about really nice mobos, LCD displays on that back that read out error codes are really nice. Unless you like beep codes and looking up what they mean, a few dollars more for a model that includes this may make a first time build experience much easier.

I've been known to be lazy and just skip the front of the case USB connections and just hook up Power. This is easier but you'll probably regret it later.

I would say if your conserned about damaging new parts when doing a self build, grab a local paper of ad trader and buy a crappy old thing, tear it apart, mix up all the bits and put it back together when you are confident sell the pos and get your new parts, they may look slightly different but tend to still go in the same places,

Case to mobo wiring is a pain if as said it doesnt match up and depending how old a rig u play about with the sata cables may get u but they just replace the pata power and data so its all good

I totally agree orcishgamer, the case is not to be overlooked. Some of the expensive ones come with reams of features (such as a front panel temperature display) though which also means reams of extra panel connectors & in the case of that one sometimes, temperature sensors. I have an Antec P180 at the moment which is a brilliantly designed case (though there are newer better versions of it.)

One thing I will say when choosing a case is not to go for style over substance. Ok all those different coloured lights etc might seem cool but they're no so much when you're trying to watch a film in the dark etc and those big fans might look good but they're usually noisy etc... best thing to do is go for a case that focuses on quiet and easy swapouts. My previous case was an XG Dragon, and it's a thing of beauty and it has some very nice features such as a slide out motherboard tray etc... but it's noisy, there's no silicon padding to buffer the fans or the power supply or the sides of the case and the fans might be high performance but they're also loud!

Also I have replaced my P180's multispeed fans now with Sharkoon 2000 "Silent Eagle" Golf Ball Fans and they are amazingly quiet; I'd recommend them to anyone wanting to reduce the dB output of their case.

I think there is a happy medium between buying a store-model and building your own and that is to go to a real computer store where you can select all the individual parts like how much RAM, what graphics card, power supp., etc. and then have the store build it for you. These stores can do it quickly and it won't cost much (less than 100 pounds). That way you get the best of both worlds - you get to select all the different parts but you don't have to worry about putting it together and you still get a store guarantee. It will cost a little more but not much. The only thing you want to avoid at all costs are integrated parts like a integrated graphics card because they are terrible.

Hybrid. Unless you're truly hardcore, a run-of-the-mill case will do you just fine. Buy a bare bones rig with a 600 or 700 Watt power supply, motherboard, and chip. That'll run you ~$500 if you're going for quality parts. Buy your own RAM, video card, hard drives, optical drives, sound card, and any other installed periphery like 15-in-1 readers or dub spinners or whatever kids do these days ;)

The RAM, video and audio cards are pluggable. The HDD and optical drives are limited to fit only way in the case, and only plug into the cables one way. You'll have done at least half the work of building a rig for yourself, saved some money, and built up some confidence so that next time you can buy your mobo and chip separately and, hell, watercool radiators off a Peltier cooler if you want.

Step by step. Next thing you know you'll be writing regexes and compiling your own kernel ^_^

Don't scare him!

I'd say don't be scared of building your own PC, it's not that difficult, it just takes time. The first one I built was only my second PC ever (I think it was a P166). I knew nothing about it really, other than having bought and installed a sound card for my first PC (which didn't come with one). I just read the instructions in the manual for the motherboard, which was much more complicated back then than it is today. There were tons of jumpers that had to be configured correctly, and lots of little plugs that had to go on the right pins. The instructions were very clear however, and it wasn't that big of a deal.

With modern motherboards, you don't even need to fiddle with things like jumper settings, it's basically just a question of putting everything together correctly. Most of the things are fairly obvious, and any questions can easily be googled.

As someone else said, choose your case carefully. Be sure to check the features and look at the design. You want to go for something that is as easy to configure as possible. My case, for example, a RaidMax Smilodon, has some nice features that makes it very easy to put everything together. Both sides open with simple pull-out handles, the HDD drive bay can be rotated sideways to easily slide in drives, and uses a rail system that means you won't have to screw in the drives, they just slide in and click into place. It has a 120mm front fan (generally, the bigger the fan, the slower it has to rotate to move the same amount of air, and the less noise it usually generates).

Sounds great, doesn't it? And it is. So naturally, I'd happily buy another one just like it, right? No, as a matter of fact I wouldn't, and here's why:

Features that help are of course nice, but you also need to look carefully at features that hinder instead. In the case (pun intended) of the Smilodon, there are a couple of things that are REALLY annoying.

First of all, the whole front of the case is covered by a hinged panel. The whole front. Including the power button, the front USB ports and headphone jacks and the optical drives. This means that you have to open the front panel every time you want to access any of these things, and as long as you're using the USB ports and headphone jacks, it has to stay open. Incredibly annoying.

Then there's a side strut bar with a fan on it, and three little rubber-tipped plastic tabs that can be clicked inward until they rest against whatever is mounted behind them, usually the graphics card. This means that there is a bit of tension between the case and the components, keeping everything steady and preventing unnecessary vibrations/rattling. This is an excellent feature, until you get a graphics card that is simply too wide to fit behind it, as I did recently. I've had to remove the strut completely (which is fortunately very easy), so now I have one less side fan. Less noise too perhaps, but also less air flow.

Finally, you'll want to try and match the motherboard and case. The SATA ports on my motherboard are placed right in front of the drive bay in my case, which makes it something of a headache to fit the cables for my HDDs.

So make the right choice when it comes to your case. Something like the BlackStorm looks like it has retained all the good features of the Smilodon, while doing away with the bad ones. The downside is that it looks like something that escaped from a Tron movie, but I value ease of use over looks. (I happen to be a big fan of Tron, but I still prefer my PC cases a tad more discreet than this). This is just a suggestion of what I might get the next time I need one. You need to find a case that is right for you.

tl;dr: Building a modern PC isn't all that hard. Be sure to choose a case that will make things easier for you, and won't annoy you during daily use.

I actually like Lian Li cases, but it's hard to recommend someone spend 200 dollars on their case...

Thanks a lot for all the fantastic responses, guys. You've certainly provided food for thought. Now I suppose it's just a matter of doing the legwork, finding the parts I need (though I now have a much better idea of what I should be looking for) and probably trawling local brick and mortar stores to spec out cases (probably this will cost more but I get the feeling a case is something that I need to see with my own eyes before buying)

I'm extremely grateful to each and every one of you for all the advice, so +rep all round

Or... ahem... I WOULD rep you all but for the life of me I can't seem to figure out how. That's mildly embarrassing

In all fairness, the cases are so good I'll happily use my current Lian Li on my next comp. It's one of the V1200 model lines (can't recall if it was PLUS II or not).
They changed the rep system to not work off the +/- thingie on posts. Still you can rate up specific posts you found helpful, they show as high rated and I think this skews searches in their favor.

Well, there are cases, and then there are CASES! :-D

When it comes to cases I find Antec hard to beat when it comes to pure cooling ability. Sure Silverstone and Lian Li make some nice looking cases and Coolermaster are the best for your water cooling but I bought an Antec Twelve Hundred and the cooling it provides is phenominal. If I was building a new system I would easily opt for the 1200's successor the Dark Fleet. It would need an additional 3 fans in the roof but once you have that you can overclock like crazy.

I bought one of the Lian Li's designed for cooling, the passive cooling and what you can get out of minimal fans in those are really good. At the time Antec was pumping out complete garbage eyecandy with moronic interior design (often requiring the longest cable runs I'd ever seen in a case).