the pentium 4 processors with northwood core ( the ones with the A behind the Core Speed f.e. P4 1800A) they overclock very stable and with aircooling up to bout 700 to 800 mhz
review of the P4 1800A @ Virtual hideout
http://www.virtual-hideout.net/artic...re/index.shtml

but you'll need some proper mobo and RAM