I would recommend :
1. Keep your old DDR2 800 CL5 RAM. (If the RAM is still healthy, no need to replace and no need to have more than 4GB).
2. Get an AMD X4 965.
3. Buy an AM2+ mobo with DDR2 compatibility.
4. Get a better GPU if you gonna use the rig for gaming. Let say GTX460, HD5770 or HD6850.
5. For stock speed A.K.A not OCed, just use the stock fan, no need for an after market proc cooler.