My whole thought on this thread is why do you need to regulate fans used for lighting?
Turn them on when the lights go on and off when the lights go off. If you want to be safe, put the fans on a different timer and run them about 15 to 30 min longer than the lights are on.
I've got an Aqucontroler and it's real nice, but I don't use it for lighting control, since a few simple cheep timers work just as well, and cost a lot less.
Controlling fans by using temp sensors and/or a computer or controller in one form or another is an expensive, and error prone way of doing things. You just have so many more places where stuff can go wrong and fail. Unlass you have some very unusual requirements, this seems to be a clasic case of simple is better.
BTW, Raido Shack sells a couple of fans that run off normal 110V AC, so they are very easy to wire into the same power cord you use to supple power to your ballasts. While they do cost more that computer fans, you don't need a 12V power supply to run them.