I played the game on a 4870x2, which can be a pain to get working right with a lot of older games due to it basically having Crossfire built-in (and not being able to turn it off). No problems here, either.

It's been a while since I played the game (over a year), so I don't remember what driver package I was using at the time. It's possible ATI did something in more recent driver updates that bugged up the game. Wouldn't be the first time. (10.6 managed to totally fubar Popcap's entire catalog, for example.) What driver version are you running?

I owned the retail version of the game prior to buying it on GoG, and I know that version hated XP--never got it to work right. I'd assume GoG fixed that in their release, though. (I got a new computer and Windows 7 in the interim, so I can't test it myself.)

By the way--disabling your card? Is a surefire way to make sure a game won't work. Your motherboard probably has limited onboard video capabilities (otherwise you wouldn't see anything on your monitor at all once you disabled the card), but not enough to do the 3D rendering required for a game, even one as old as Sanitarium.

The XPress 1150 is an old card, too--from 2006 according to wikipedia, and a laptop model to boot. That might have something to do with it...although again, with a game as old as Sanitarium, I'm not too sure that's the cause.