Likkerpig, try uninstalling SP2.
Some folks, though with Athlon 64 systems, have had major issues with SP2, such as crashing and slowdowns.
While I had heard that the Barton series chips work well with that update, you never know.
Anyhow, it may not be a millionaire's system, but my friend, you built yourself a pretty nice rig there. You've got a fast chip, a powerful video card, lightning fast HD, lots of RAM, and ample power (boy, I wonder what your case looks like!). When you've got it going smoothly again, enjoy it.
(I built a similar system for my son, who plays more serious games than I do. I mess with SFC; he plays AOM, etc. I gave him a 2500+ Barton, Radeon 9500 (not flashable, alas), 80 Gb ATA-133, 1 Gb RAM, and also 420 W. AOM runs very well on it.)