If you don't mind me saying so, this system:
AMD Athlon 64 2x 3800+
Western Digital 250GB
Ati Radeon x300 @ 421/220
is a complete mismatch of parts if it is to be a gaming system. You have spent quite a bit on the dual core CPU but completely wimped out the the graphic card. At $200 that x850xt is a really good deal but I think a 7800GT would be worth a look. The GS should be out of the question for this system.