How do you make a perfect circle in PS CS 2?

I have a black circle and I want to cut a perfect circle in the middle of it so that the circle cut out is white (or background color).

I don't care much if it is in the perfect middle, I more just want to know how to make the perfect circle cutout. Not interested in textures, bullet holes or anything fancy. Just a circle cutout.

Thanks in advance.

on the window with all the tools, the top left one is a square. right click it and select the circlet one, and then make a circle. after you make a circle hit delete and the space inside the circle goes poof~

Thanks it works!