Okay get the latest drivers for your SIS 661 here: http://www.sis.com/download/download_step1.php
try running with the new drivers if that doesnt work try unistalling DO, reinstalling, running the hardware troubleshooter tick force 3d, no power vr, no 3dfx, and forcemmx render.
Then right click on the DO shortcut, properties, then compatibility tab and select run as admin, and in win 98 mode.
Tell us if that fails / succeeds
try running with the new drivers if that doesnt work try unistalling DO, reinstalling, running the hardware troubleshooter tick force 3d, no power vr, no 3dfx, and forcemmx render.
Then right click on the DO shortcut, properties, then compatibility tab and select run as admin, and in win 98 mode.
Tell us if that fails / succeeds
This helps a lot; thank you! With the updated drivers and the troubleshooter options you suggested, the game now runs and I can get to the menu screen, start new campaigns etc.
The only thing left to fix is this: When I start a new campaign, the units show (and the talking heads in the bottom left etc) but the landscape itself is completely black. But I think I saw something else somewhere on this site about how to fix that...