They're called tri-wing screws. You will therefore need a tri-wing screwdriver. They're about $5 from eBay, not counting shipping.
Tri-wing screws that are on the surface of an object can be removed without the screwdriver, though. I removed the screw from a GBA cart by jamming a flathead screwdriver into one of the wings and pushing.
11/04/2007
I'm in your profile, deleting your spams for Great Justice.