"Fatal Error", won't intstall

Sorry for creating a whole post just because of this, and for not thoroughly searching to see of this had been resolved, but I have a problem. I can't install the game; on the step right after when I select the directory to save to, it simply says "Error" and quits. The thing is, I installed the demo a while ago and it worked. I uninstalled it because it was really hard to get anywhere in addition to the games ending after preset amounts of time. Recently my friend asked if I wanted to get the game and play online with him, so I beefed up on some strategy and tried installing the demo. Unfortunately, it didn't work (presenting me the same message I got just now). Not wanting to buy the game and have it not work, I asked my friend to bring his copy just to make sure everything worked. Well, apparently not.

Specs: Dell Inspiron 1525, 2 GB RAM, 1.7 GHZ Intel core 2 duo, Intel GMA Mobile 950 card. However, I'm highly sure stats aren't the problem because this PC can actually squeeze by World in Conflict at minimum settings with a decent framerate, and Guild Wars at max no problems. I do have Vista, but the only problem I've ever had before was the Homeworld 2 demo failing to start. Yes, I have tried the compatibility wizard multiple times and on different settings.