i've got the P4 3.0ghz @ 3.6 on a stock HSF and its usualy only 3 deg more hotter than stock, you should be fine with the stock fan but just keep an extra eye on the temps as prescott's are know for thier heat
the best way to O/C is through the BIOS and look for the FSB speed, increase this at ONLY 2-3 mhz at a time, reeboot run a demanding game test (3dmark) and continue whilst watching your temps.
im sure theres other ways to overclock but this works dandy for me
Hope this helps a bit
P.s What are your other system specs?