i had always use computer fans for quiet cooling too. its only $2-5 a fan. u just need to get any ac-dc adapter (3-12v)the higher the v the faster the speed.
however, i dont use them near water due to moisture problems.
Thanks Xoomer... Was going to do this on my 20" NEP. Any particular reason why the factory power source can't be reused?
If you are referring the power source of the Current fixture, the fans are usually 110V AC and thus the power source cannot be directly put into the 12V DC fans.