1) When you installed Windows 2000, was it a fresh install (i.e. the hardrive was formatted prior to installing the OS)?
Yes!
2) Have you re-installed the drivers for your graphics card?
Yes...
3) Have you played any other games apart from A4 & Geneforge 4, if so, does this problem also occur?
I played Geneforge 1 to 3, Avernum 1 to 3 too. No problems. but avernum 4 and geneforge 4 i can't play or start the game.
4) If your display is 800x6500 and cannot go higher, you're out of luck. The Geneforge engine (which is used for A4) requires 1024x768.
Argh! >.< I need to change my monitor to play G4? ah... Ok, thanks.