I have a 6600 GT AGP from MSI. I installed the new drivers after reformating my comp after a virus breakdown. After that any program runned by valve with the steam engine has missing text and graphics. This problem goes in and out. I go into like counter strike source and the backround is all screwed up and the text is very hard to read. Then other times the text is kinda easy to read and i am missing no textures.

Its just random! It does it with anything using the source engine like i said, Ex. counter strike source, HL2, Garys mod, HL2 Deathmatch etc.
I am running on older drivers now and the prob is still there, i got omega drivers and the same problem is there.
Any help?