Lillycake: Thanks. I'll make the post later, I'm way to angry to deal with any of this now.
AFnord: Here are a handful of possible solutions:
Install the
Widescreen mod (issue might be resolution dependent)
Change to 16bit colours in Windows
Enable/disable openGL acceleration in the config menu
Change to software acceleration for all individual options in the config menu
Don't forget, try switching the game to windowed mode (alt-enter should work) and you should be able to move the game window and find the message box to read what it contains.
Another thing - all Infinity Engine games (and almost every other pre-XP game) need to be able to write in their own folder, Windows Vista and 7 has a problem with this if you install the games to Program Files, so try installing the game elsewhere or running as Administrator.
Lillycake: Sidenote, I bought the game and 10 minutes later I got a call from my credit card company saying there's possible fraud and an investigation is pending. Not sure what that means. (I downloaded the game successfully but it's not working at all.)
Several banks automatically flag transactions to GOG simply because they're incorporated in Cyprus (also, their offices are in Poland, and the payments go through the UK). Just try to make them understand that GOG.com is a respectable company, and you shouldn't have more trouble.