How to power a PC fan?

Searched the forums and have not found an answer. How do you connect a computer fan to a power source if you use it for your grow box?

I have a power adapter for a mp3 player that was stolen... and it converts to 9V. Would that be an option after some soldering?
Thanks for any advice.

That'll be perfect, most pc fans are 12v. Any charger from 6v to 12v will work. Cut off the plug and strip the wires. There's usually three wires, the green one is a ground, the black and white are power (or any color other than green). Just connect the wires to the fan. If nothing happens switch the wires, you can't hurt the fan. That should get it running. Good luck.

or if you have an old pc power supply you can http://www.techwarelabs.com/guides/misc_mod/psumod/

Awesome, thanks!