Expanding? Hm. They shouldn't be expanding.
Here's approximately how I beat this mission on hard:
The first part is self-explanatory, use the firebats to burn your way to the base. Remember to pick up any mineral and gas pickups you see off the road.
While waiting for the first truck, get the SCVs going and build more SCVs. Start getting marines out. A bit before the truck starts, send your force up the road. You'll discover the first bunker. Let it be for now and wait here for the truck. Escort it to the end, then head back to the first bunker.
Build one more bunker here and fill them with marines. There's another spot on the right side of the road, also place two bunkers here and fill with marines. Finally there's a spot on the left side of the road almost at the starport. It'll take you 2-3 passes to get all the bunkers up and filled with marines, so use mercenaries for escort. Once you have bunkers blocking all entry points the mission is a breeze, however keep the escort to fend off any ambushes (there are some on hard at least).
The collectibles for the side objective are further in the map at the first and second bunker spot.

First, let me get something out of the way. I think I played maybe 30 games of the original Starcraft's standard multiplayer mode. It's far too hectic and stressful for me to fully enjoy it. However, the custom maps are truly where it (and Starcraft 2 more so) shines. The Starcraft 2 map editor lets people do anything. There are shmups, there are horizontal beat em ups, people are making third person shooters. These are things you can just boot up SC2 and play with a bunch of other people. It's tons of fun, and is where SC2's true replayability comes from.
Also, the single player campaign is incredibly polished. Every mission has some quirk that makes it unique. Whether it is that lower levels get flooded with lava every few minutes or that you have to escort a vehicle. What makes this escort mission fun? This vehicle is covered in weapons and just needs you to repair it and provide some aerial support. Every mission is something new.
The plot is also very intriguing. I'm not going to spoil anything, but the plot (at the point where I'm at in the campaign) has some interesting twists and turns and it really makes you want to play it to find out more. You can also go around and talk to characters between missions, which is very well done.

Holy crap is it getting hard now. The final missions are very, very brutal in difficulty.

Pros:
Custom maps are awesome
Ranked games if you're into that
Awesome single player (mission variety, ability to talk to characters between missions)
Don't have to be online for single player
Fun
Custom maps are stored on Blizzard's servers so you don't have to worry about not having the map locally
The map editor is the coolest map editor ever
Difficulty options for the SP missions (if you've played the original SC or BW you'll appreciate this unless you're far better than me)
Awesome soundtrack
Cons:
No chat rooms as of now (they're going to add them in a patch soon)
Custom game system can be wonky, since most people don't look past the first 10 games, so it can be hard to find people to play less popular maps with
Only one username online
No inter-region play (although I think you can change your region at any time on battle.net)
No custom kill animations (some people notice this)
No LAN
Pros/Cons: (depends on your point of view)
If you played StarCraft you will have a head start on SC2 because many of the mechanics are the same
Achievements (some love them, some hate them)

Thanks! I'll be sure to try that strategy when I return to that mission.
I'm thinking about buying the strategy guide, because my multiplayer tactics are abysmal. I just work on building my base up when all of a sudden my opponent has many, many ships and tanks headed towards me. Maybe I'll try the "Zerg Rush" strategy people have talked about?
I usually loathe strategy guides, but this game actually requires strategy.

Thanks, good information. I found some other info as well so I'm off the fence now . . . =)

A great beginner strategy is the terran reaper rush. Get two reapers out as quickly as possible and send them to your opponents mineral line. If he has low or no defense there, the game is basically won as you kill all his gatherers. Even if he doesn't surrender, you'll have a big edge for the rest of the game.
I usually have the following build order:
SCV - Barracks - SCV - Refinery - SCV - SCV - Supply Depot - Tech Lab - Reaper - SCV - Reaper (send out the reapers) - Factory - Supply Depot - Starport.
If the rush fails I can then proceed with advanced units from the factory / starport.

Anyone has a spare guest pass? :)

If you give me your email I'll send you one.

Same as my username here at GOG, just add dot com. ;)

at what dot com? gmail? hotmail?
I don't think (yourusername)@.com will work =P

I failed. Sorry, forgot to write the "live" part. :)
KavazovAngel at live dot com. :D

Sent.

Thank you very much! :D But before I use it, is there a way to change the region, since the game's activation page shows that the region is NA?