when I built mine I was on a tiny budget. Turns out I built the most stable machine I've ever used.
Amd X2 4000+ (75.00)
2 GB mushkin DDR-2 800 (100.00) (just saw newegg has Corsair 4gb for 80.00)
Abit NF-M2S MB (75.00)
Radeon X1650 256mb (does ok for 75.00)
520 watt PS (80.00)
320 gb seagate 7200/ 80 gb seagate 7200
XP home
Had this for 2 years never reformated or had any freezes.
can run Internet, Photoshop, MP3's at the same time with no slowdown.
Closest I got was 3000ph X 2000pw and 40 layers took about 15 seconds to save.
If price is not an object go quad, otherwise dual Amd should work just fine. At about half the price of intel it's a bargain.
From your list-
asus M3N-H-HDMI -133.00
AM2 x2 5000+- 74.00
4GB Kit-800(2x2G) kingston- 103.00
512M 9600GT MSI (optional)
Seagate SATA 250gb / times 2 -59.00 x 2
ASUS VENTO TA-861(nice looking case, see if the'll swap for a 500/550 watt PS)- 75.00
Total- 503.00 not bad