with the 92MM tornado, you will have to use a fan controller. I recomend you get a decent one too, my 92MM tornado burnd out a cheap fan controller I had bought from compusa.
to be able to control fans from the bios, or from a program called speedfan, you have to use the motherboard fan headers. however, these fan headers do not have enough power for a tornado or a smartfan 2. it would work at first, but eventually the headers will stop working
It would be nice if the BIOS had a fan speed control. I don't expect to see that anytime soon.
A very simple fan speed mod is the ThermalTake Fan Speed Controller. It fits into a PCI slot and has "Hi" "Med" and "Low" settings. $10. Easy to install, it's just plugging things in.
You can make your own with a rheostat. (A 10-watt rheostat that goes to 50 ohms will do you.)
You can control all your fans in the box with a big fan controller that goes in a 5 1/4 bay.
You could put a 10-watt 30-ohm resistor in the fan circuit and you'll probably have a fan that still turns, but a lot slower.
You can 7-volt-mod a fan by connecting the red fan wire to the 12v yellow PS wire and the black fan wire to the 5v red PS wire (referring to the colors on the 4-pin connectors from the PS that go to your hard drives etc.)
O wait, I forgot, there are also fans with thermal sensors that go "fast" only when they are "hot".