All PSU's will fit as long as it's an ATX.
Well, keep this build right here that you've posted.
Newegg.com - BIOSTAR TFORCE 550 Socket AM2 NVIDIA nForce 550 MCP ATX AMD Motherboard - Retail
Newegg.com - AMD Athlon 64 X2 3600+ Brisbane 1.9GHz 2 x 512KB L2 Cache Socket AM2 Processor - Retail
Newegg.com - G.SKILL 1GB 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Desktop Memory - Retail
Newegg.com - FSP Group (Fortron Source) AX400-PN, RoHS, 12cm FAN, version 2.2, 2 SATA, 20+ 4 pin, PCI Express, 400W Power Supply - Retail
Newegg.com - EVGA 256-P2-N615-TX GeForce 7600GT 256MB 128-bit GDDR3 PCI Express x16 Video Card - Retail
This build of your's is great.