I have the Swiftech 462A HSF. It comes with the 80mm Delta which can be pretty loud also. I bought the optional rehostat from them that allows me to control the speed of the fan. You should be able to get one at Radio Shack but I am not sure which one will work. Hopefully someone else will chime in with that answer.
There is an article on the front in Tips and Techniques, called, I believe, Relays and Rheostats, that will show you what to get and how to do it. What I don't understand is why you would want to slow down one of the most powerful CPU cooling fans going. You are much better off buying a cheaper, quieter fan to put on your heatsink, and selling the Delta if the noise bothers you.