a good cooler is must when you are overclocking, it virtually decides the limit of your overclock.
a better cooler will yeild better overclock. Swiftech ones and OCz Gladiator are good ones. Maybe other people will recommend a few more.
still, you can do with the cooler you have, you would get the idea, that there is still some potential when a better one arrives!
<font color=red>No system is fool-proof. Fools are Ingenious!</font color=red>