Big F. up! Anybody had similar issue?

Well, I have a new PC. Its quite high end. I have 4400+ X2, A8R32-mvp Deluxe, 2 gigs RAM, X1900xt. Still when I play Source games, BF2 i get great problems. When I start a source game it usually plays nice for 4 to 5 minutes then it hangs, (stutters, freezes whatever you want to call it). Then it feals it must do that every fifth second, so it hangs for five seconds and then it plays for five. Really annoing. I have read alot of fix suggestion on internet, but none seems to help. I have tried affinity, the new friends beta, tinkering with sound loading, I have the latest drivers for everything, tried 3rd party drivers. I dont have a sound card, I use the onboard sound chip. Other games work fine, like Oblivion, Quake 4 and so on. I heard that FEAR, BF2 and Source uses the same texture loading system, so that could be the problem. Please help, I am stuck....