Athlon 64 3000($155)
Asus A8V-E Deluxe($170)
1 GB Corsair Value Select($130)
eVGA GeForce 6600 GT PCIE($192)
Seagate Barracuda 160 GB HD($109)
CM Centurion 5($80)
Antec NeoPower PSU($125)
That's all about $960, a tad over budget but I beleive it should be quite upgradable. Also the Centurion 5 comes with a 350w PSU but I'm not sure if it has a 24pin connector for the mobo or a 6 pin connector for the PCIE video card, and adapters are annoying to find if you ask me. As for a the CD Drive, you can probably use your current.
BTW, all the prices are from www.newegg.com
you should also compare with www.zipzoomfly.com
Also if you plan to do any overclocking I'd go for an NF4 Chipset mobo such as the DFI Lanpary UT NF4 Ultra D
for $144 on Newegg.
Enjoy your build!