If you do decide to use a PSU: http://forums.slickdeals.net/showthread.php?t=939108

Newegg has OCZ 2GB (2x1GB) DDR2 800 (PC2 6400) Desktop Memory for $19 after $25 Rebate.
They also have OCZ 500 Watt ATX12V Power Supply for $45 after $20 Rebate.

If you purchase both as a combo, you save $20 and pay $44 for both after rebate with free shipping