I used to have an old Dell XPS-P90
Pentium 90MHz tower computer back in 1994. The CPU only had a heatsink, no fan, and got hot as hell!
Actually, he's talking about this : http://www.newegg.com/app/ViewProduc...109-119&depa=0
Since the heatsink is 96mm x 96mm, i'd suggest you get a 92mm x 92mm fan, such as this one : http://www.newegg.com/app/viewproduc...180-053&DEPA=0
It moves alot of air, but is relatively loud. Look around for another quieter 92mm x 92mm fan if you're worried about noise.