So I have this problem, I have an old computer with a motherboard that runs AGP x8 and I can't afford changing most of the components. I have an Asus Radeon 9600SE 128mb, and a friend gave me a Geforce FX5500 256 mb. I thought that it would be a better card then my previous one but from what I've seen its only worse. Games that previously worked, are screwed up now and have these strange texture problems.
Had a similar situation a couple years ago, I was running an FX5200 and my uncle had a spare 9600 lying arround, so I thought 'O yea, thats gotta be better'
Turns out even the crappy 5200 was better off. Sounds to me like driver issues. Grab a copy of DriverCleaner, uninstall your drivers, run the cleaner for both ATI and nVidia, reinstall your drivers and see how it treats you.
Well i tried to simply uninstall the drivers for both cards, then i downloaded driver cleaner pro and used it to uninstall the drivers or whatever was left of them. Then i installed the fx 5500 driver and tried again...and there is no difference. I tried playing Left 4 Dead which my 9600 could handle on 640x480 with low settings, it was definitely playable and enjoyable. Now with the FX 5500 all i see is white triangles and other shapes. The whoel screen is full of them.
Here is a screenshot of what I encounter in game. And there is no moment in game where the game looks anywhere close to what its supposed to look like.