[Christ]

If you've got a dremel, you can use that for the tops, you just grind off the "lip" of the can all the way around. Actually, any grinder will do it. Then grab the mouth of the can with a pliers, and pull vigorously.

For the bottom, a belt sander. Sit the ridge on the belt sander until it cuts through, and you just lift the can afterward. Again, a grinder would work as well.

If you want to use a hole saw, you need to use a very low speed drill and very little pressure.