I was bored at work so:
CPU: AMD X2 4200+ AM2
http://www.newegg.com/Product/Produc...82E16819103747
MOBO: ASUS M2N-E ATX
http://www.newegg.com/Product/Produc...82E16813131022
HDD: WD 160GB 16MB SATAII
http://www.newegg.com/Product/Produc...82E16822136009
GPU: eVGA Geforce 7600GT KO
http://www.newegg.com/Product/Produc...82E16814130017
RAM: OCZ Gold 1GB (2x512MB)
http://www.newegg.com/Product/Produc...82E16820227029
Total is $625.96 which leaves some moeny for Case, PSU, and Drive. If you cant fit the rest of the components in, I would downgrade to an X2 3800+.