If you wanna do this as cheap as possible, Killerbug posted this in a different topic (Fan overclocking)..
The grey wire is the 3.3v but I can't remember the colour of the 12v wire. You basically take power from the 12v and convert it to 3.3v which you connect to the grey wire (only the wires going to the fan need to be touched). I'm using a very similar method (I use an external power supply right now, powers lights etc for me too), this way the fans run either 100% or stock. You can add a switch, so they run normally, but flick the switch and they run 100% or just wire it up so it's permanent.
Originally Posted by Killerbug
oralphie: Will this allow chuck norris to play backups??? PLZ HELP!!!