modding your mouse look plz i need help

ok i need to know were i can get this size fan and how big is it

http://metku.net/rottaflekti/index_eng.html

That looks like an 80mm or 60mm fan. Personally I wouldn't go through that trouble. Just get a cheap 10$ Nyko 800 DPI optical. comes with fan

it's a 40MM, and I've done it.

Do do it for the fun of it, go ahead, but for usability I say go for the Nyko. It's a cheap, shabby piece of kit but it does have a fan built half-ass in already.