my receiver only has a two prong connection in the back, and my computer power supply has a three. do you guys just rip off the extra ground and connect it?
Probably not a good idea to plug a PC into your receiver. The AC plugs on the back of the receiver should be reserved for playback units (tape deck, DVD player), which don't soak up a lot of electricity per normal use.
1) NEVER strip the ground off any 3 prong device. There's a reason it is there.
2) As Patrick mentioned, the outlet on your receiver has a max rating (check your manual) that is generally pretty low, and a PC power supply will almost certainly exceed that rating.
the amount of electrical noise that a computer power supply introduces into a circuit (especially a receiver) is phenomenal. add fans the the mix and you just added 50+dB worth of electrical noise into your receiver. not the "best" thing to do.
Using an entire ATX power supply to run some fans is just huge overkill, not to mention unwieldy. Go down to your local electronic supply store (RadioShack works fine, if overpriced), and pick up an AC/DC converter (sometimes called a wall-wart or power brick). Most computer fans run off 12V, but if you want to slow (and quiet) them down run them at 7V instead. A voltage-selectable converter works nicely for experimenting and manual control. Depending on the current output of the converter and the current draw of the fans, one converter should easily run a number of fans, just splice the wires to run them in parallel.