get one of these suckers if you want to O/C hardcore style
http://www.tomshardware.com/cpu/20031021/index.html
there are many systems like this, you need to keep the CPU really cool (below zero ideally). have a look around Toms Hardware
check this one, P4 @ 5ghz :
http://www.tomshardware.com/cpu/20031230/index.html