I want to use my old computer fan and i was wondering if its possible to power it off of an external battery. And if so whats the best way of going about it.

You wouldn't be able to use a small battery like a off the shelf 9 volt. A standard fan could drain one in about 5 minutes. If you really want to I'd assume you'll need to use a lantern battery of something.

you COULD hook up an additional power supply. http://club.cdfreaks.com/showthread.php?t=111640 check there to start. p.s. i did this and it worked fine.