are you tryign to make holes so you can mount the fan to your case? my suggestion is look at the screws you are using, and then take a drill bit and put it in fornt of teh screw, so the drill bit is infront of the screw and when you look at it strraight on all you see are the threads of teh screw....
start small with the hard drive and then slowly increase the size until it comes out... be careful!