Not Happy!!!

Can Somebody please please help.
Getting Corrupt GFX and textures in Unreal 2, Splinter cell and 3DMark03 to name a few and im tearing my hair out!!

System Spec
Athlon XP 1800+ (1.5GHz)
Via Apollo pro KT266a (266fsb) (Latest 4in1 Hyperion Drivers)
256mb PC2100 DDR Ram
Radeon 8500le 64mb with CAT3.2 Drivers
SB Audigy
DirectX 9
Windows XP Home

This is very fustrating as my rig is very speedy (NO Overclocking) but alot of games especially Unreal 2 just crap textures and bad graphical corruption....any advice please