Do you want to upgrade your video card to pci express ?
(9800xt is not bad but pciexpress is the future and the future is now )
if so you could get the latest intel 775 cpu like p4 530 (3ghz)
on a asus p5gd1 (easy overclocking board) not very costly.
I have a p5gd1 and p4 530 overclocked at 3.3ghz with standard pc3200ram no heat stable and very good cpu performance.
check the cpu score here those are overclock p4 530 bench on asus p5 series board (i am the one wiyh the 6600le video card.) notice the front side bus speed of 220+ must multiply by 4 so 880mhz+fsb