Games fall back on Win XP and Win 2000, WHY???

[Honzyczech 0]

I have AMD Thunderbite Athlon 1.2 Ghz, Motherboard ABIT AT7K RAID, 512 SDRAM, GeForce (MSI) 4 Ti 4400, and games fall back to windows XP and to Windows 2000. Why??? I have new detonators 40.72, new drivers for sound blaster live!, VIA4in1 4.43. For Win 2000 install SP 2 and for win XP SP 1. Where is problem??? I heard, that new directX 8.1 may doing problems with AMD processors. Is that true?? I tried to install 8.0 and tried to run games, but if i looked to my directx status, still installed 8.1. Could I uninstall DX 8.1 and try 8.0??? Have somebody any idea??? Please help me. Sorry for my poor English, I´m from CZE...Thanx