Newer games don't work...

[Darkhound]

Hey guys, hope someone can fix my problem. I got a new pc (AMD Athlon xp-m 2800+ (overclocked to XP3600+) with a Radeon 9700 (overclocked to 9700 pro), 1024 MB RAM using WinXP pro SP1 and Direct X 9.0c. So far, so good, but since I got my Radeon, every "newer" game like D**M3 or "Halo" cannot be played They start, but afetr a short while, I got told "Program xyz caused a problem and must be closed." (Sorry, I'm german and in german language it maybe sounds a little differently). Then the os wants to send a failure-report to Microsoft. But how the heck could they help me? I've the newest Windows-XP, some kind of good CPU, enough memory, a more or less actual grafics-card (with newest drivers installed), but those games simply don't want to work. What can I do?

Thanks in advance, Darkhound