Flashing Graphics

[Panhead328]

Well, I've searched all over the forums (and google) and I couldn't find anything exactly like this. There seem to be a lot of problems with the Intel cards on here, but I'm wondering if there is any way to fix this.
When I first tried to play the game, I got the whole "unsupported graphics card" message, and after several help pages and tutorials, I was able to make that go away. Then I had a problem with shadows or lighting or something like that, and I was able to fix that, I think, because I set the resolution to fit my monitor.
Now, however, I have a problem with the whole landscape flashing in game. About once every second everything just disappears except for the sky, the HUD and any character models that happen to be on screen. It happens real quick, but it hurts to watch, and it almost makes the game unplayable.
I couldn't find anything about this exact problem happening before, so if some screenshots are needed, I'll post some later. Thanks.

Linux Ubuntu 9.04
Mesa DRI Mobile Intel GM45 Graphics Chipset GEM 20090326