Well, tonight I hit the point where I think I'm ready to go for 7 after being on XP (do NOT suggest Windows 8, I don't want it, plain and simple). I'm tired of only being able to use half my RAM so its time to upgrade to a 64-bit OS. But I'm stumped on a couple things...

First, what programs will I not be able to use on 64-bit? I mainly use my PC for MMOs and such, as well as older games (both GOG and disc). Most newer games don't interest me due to DRM schemes, so I don't bother with them. Is there a list somewhere that says what won't run on it?

Second, is there any real difference between buying the Upgrade version of 7 Home Premium and the full version? There's an ~$80 difference between the two, but what is really different? I know the OEM/System Builder version is limited to one hardware configuration, apparently, and since I tend to tinker, that's right out.

Thanks in advance.

There's not much that won't run on it except older 8 and 16 bit games. I've got Win7 Pro 64 bit installed on my rig and have yet to find a game from GOG that I can't run on it, and I've had no issues with games through Steam, Gamersgate, Indie bundles etc either. It's tied to your motherboard, actually. I've added and removed several hard drives as well as switched video cards a couple times in my rig and not had any issues (OEM copy). I'm not positive, but I think the only difference with the upgrade is you lose your XP license when upgrading. If you buy an OEM copy of Win7, you'll still have a valid XP license in your pocket.

Windows 7 (64-bit) is set up so 32-bit and 64-bit programs will be able to run on it. You may run into some problems with older programs, but most of those can be fixed with Compatibility Mode. I'm not entirely sure about this part, but I think an Upgrade version takes all your old files from XP and stashes them in a special folder on your new Windows 7 installation partition.

(If I'm wrong, somebody please correct me.) You're welcome for my first answer. It's kinda premature for that yet with my second... :P

I once knew of a compatibility site (from the Vista days), but I can't find it now. I'm not sure if it's even up to date.

A lot of the trouble with Windows 7 is old DRM not running. MMO and GOG games should run.

An upgrade version requires a previously installed OS. I think it will "eat" your XP license, so if you're interested in running the two OS's with dual boot, that would be a problem. If not, then it's okay.

I switched from XP to Win 7 RC2 (skipped Vista) when it first came out and have since noticed very few detrimental effects. Some programs can be nuisance to get to run, but emulators and built-in compatibility fix most of those. The last thing I didn't manage to get running was Cyberia 2, but I didn't spend too much time on it. Probably doable. And your MMOs will be fine.

Basically, do make the move. I'd never go back to XP after having used Win 7.

e: and needless to say, GOGs are Win 7 compatible.

There are 2 kind of OEM. Brand OEM (eg Fujitsu, Dell, Toshiba) and no-brand OEM. The brand OEM contain an array with a key for the installation, that checks the BIOS (aka motherboard) for a matching array. If the two arrays verify an equation, then Windows is activated without doing anything else.
No-brand OEM (and normal versions of Windows) do not contain that array, thus require normal activation (internet or phone).
You can use a brand OEM version with a different brand motherboard, but you'll have to activate windows normally.

P.S. For more info, check the "My Digital Life" forums, and look for SLIC threads.

The upgrade version is perfectly fine to buy. You can do a clean install numerous ways using upgrade media. I've done it 100 times. It's definitely best to buy the upgrade version to save a few bucks. Don't buy an OEM version though, but others have covered that. And as others have said, the majority of your programs will work fine with 7, either natively or by running the program with certain compatibility settings which you will be able to set by going to the properties menu of executable files.

Once you get a copy of Windows and are ready to format, feel free to contact me and I'll be glad to explain the various ways you can do a clean install if you wish. You can always just do an upgrade install if you want, but I don't recommend it.

NOTE: I just realized, if you decided to upgrade to 64 bit, you WILL NOT be able to do an upgrade install over a 32 bit version of XP. So, just contact me once you get the disc for Win 7 and I'll walk you through it. Also note that Windows 7 license keys work as both 32 bit and 64 bit versions, even if the disc you have claims to only be one or the other.

Also, to the best of my knowledge, upgrading has nothing to do with eating the previous windows license. You would still be able to reinstall XP using the same license key if you decided to downgrade.

The difference between the upgrade version and the full version is that the upgrade version requires you to have a previous version of Windows installed and activated, whereas the full version doesn't.

You can still install an upgrade version without having that prerequisite (basically you install it, fail activation and then install it again over the previous failed install) and be OK.

Most games and programs will run fine on Windows 7. Windows 7 does actually have a great compability, there are only a few games that i couldn't get to work on Windows 7.

However, if you want to be 100% sure about it and hav no issues about compability at all, i suggest you keep a dual boot system. I don't know how the upgrade works on Windows 7 (whether it kills or not your XP partition), but i do know that Windows 8 allows for a clean install even if you use the upgrade version. If the upgrade version doesn't allow a clean install, then you wouldn't be able to keep a dual-boot system.

I have a dual boot system myself, i have a XP 32 bit and a Windows 7 64 bit partition and it works perfectly. I have a few older games (physical copies, not GOG versions) that do not work on 64 OS (they don't even install, actually), such as Dark Earth, KKND 2 and Chasm. They do work on my XP partition, though.

Like ET3D said, there are a few not so old games that have issues running on Windows 7 x64 thanks to the DRM not being compatible with it. One example is Rainbow Six Vegas, which uses an old version of Tages that is not compatible with Windows 7 (it wasn't out when the game came out) and there is no official patch for it. You can get it to work with an userpatch, though.

On the other hand, i have never found any Steam or GOG game that didn't work on Windows 7. The only issues that i've had were with older physical games. Oh well, in that case, you should just make a new partition and install Windows 7 on it. You'll be able to keep both OSes in your PC.

Remember, you can install Windows 7 AFTER XP because it recognizes older Windows versions, but you can't install XP after Windows 7 because XP does not recognize versions that came after it. If you do install XP after Windows 7 the MBR table will be overwritten by XP, making Windows 7 "invisible" to the system. It is possible to get Windows 7 working again and install the MBR for it, but it's a royal pain in the ass to get it working.

You can't actually do that with an upgrade copy of the OS easily, at least I don't know anyone who tried that. The reason is that during install it detects that you already have a copy of Windows installed and it gives you the options to either upgrade (which in Fomalhaut30's case wouldn't apply anyway, as he's going from 32bit to 64bit) or wipe and install.

Sure, you can then install Windows XP again and hope it will activate and not de-activate your Win 7 copy.

It should be noted that an Upgrade version is licensed as a replacement for the previous version of Windows; running it alongside the version it is supposed to be replacing is not a valid licensed use. System Builder (OEM) and Retail licenses do not require a previous version so are valid for dual booting alongside any other properly licensed version(s).

That being said I don't see the value of an XP partition. I initially kept mine when I installed the Windows 7 beta but I removed it very soon after that because I never found any need for it. There is hardly any software that worked on XP that you can't get working on Vista, 7 or 8 with little or no extra work.

Well, I don't think there's one true answer, so I gave +'s to all. :)

The only games I could run on XP but have not been able to run on 7 are two old Lucasarts games, Shadows of the Empire and the first Infernal Machine.

Most games on GOG work with Win 7 64 bit with a few requiring minor tweaking. You will find a thread in each game's forum subsection with what to do to get it to work.

There is no difference in upgrade vs. full version because the upgrade version of Win 7 actually contains the entire OS.

MMO's work beautifully in Win 7 and some of them, specifically lotro and DDO have dx11 options which you can take advantage of if you have an applicable graphics card.

Hope this helps!
~Cym