Hoot's got a great point and unlike most engineers, I think the same way. None the less, I have had good luck with the 25 ohm rheostats at the Shack and 120 mm fans. I would recommend a voltage regulator over any rheostat though. That's the "Hoot" in me comming out. The only rheostats I have installed in computers are for friends that won't pay a few extra bucks for a voltage regulator circuit.