3 wire computer fan won't run continuously

"Well, you do need 12V for the fan to really kick. Check the image on the link you provided again :)

Anyways, feeling adventurous? Here it is:

Instead of fiddling around the motherboard you can splice the fan wiring with a free 4 or 3 pin molex adapter coming of your power supply unit.

There's 2 ways. I'm explaining the more difficult and leaving a note on the easier:

On the fan:

Remove the isolation of the end of both the Red and Black wires, thus exposing a little of the metal wire beneath.
Bend the tip of the exposed wire, producing a tiny U shape.
Clean and isolate the white wire. You won't be needing it.

On the PSU: (assuming a 4 pin molex)

Clip the wires on one of the free
molex adapters, removing the adapter
entirely. These things are becoming
useless these days.
Isolate the Red and one of the two
Black wires. It's the 5V cable and
one ground. You won't be needing
them.
Removing some of the isolation from
the end of the remaining yellow and
black wires (12V and ground).
Bend each of the tips of the exposed
metallic wires into a small U shape.

Finalize:

Hook up the fan Red wire with the PSU
yellow wire.
Hook up both black wires
Cover each with electrical tape

So you just hooked your first 3-wire fan to a 4-wire molex. What's easier than this?

Use a 3-pin Molex instead, hehe. Just
don't forget. On your PSU all yellow
wires are 12v and red wires are 5v.
Go to an electrical shop and buy pins
that fit into your molex. In this
case you can attach the end of your
fan wires to these pins, wrap up in
electric tape for extra firmness and
simply attach the pins to the molex
on the right positions (as above).
You saved yourself removing a molex.

Finally, what you have been waiting for: As for our motherboard

Read the instruction manual and check the available connections. You are after a 3-pin connector on the motherboard with the following setup: Signal-12V-Ground. (In this order I believe. You can read signal or CHA_FAN_SPEED on the manual. Mine reads ""signal"")).

It's harder to connect to the motherboard as you may guess. These connectors are small and it's tough to securely attach your wires to them without a) buying a adapter yourself or b) go Rambo on it and solder the thing.

Have fun!"

"Look inside the exhaust port of the fan. You will see a small blue or green thermistor. This controls the speed of the fan. The fan starts slowly and as the air coming out of it warms, the fan will increase in speed. As the air again cools, the fan will slow.

This is done so 1), it makes less noise, and 2), it draws less current when it's not needed. Pretty nice feature if you want to cool something using a 12 V battery. I use them to cool the heatsink on Peltier modules. As the demand goes up, the fan increases speed and cooling. The red and black wires are + and - 12 volts DC, the white wire is for the tachometer output. You can ignore the white wire if you don't need feedback from the fan concerning its actual speed."