There are many instructionals on this project available on the net (see links below).
As far as I can see, there are two schools of thought on this: saw off the bottom, or knock it out. Which method you choose depends on which tools you have and how big you'd like the opening of your vase.
Either way, you have to get the center part out. That black piece on the bottom is actually a dark, purple glass. White bulbs are actually coated with a powder on the inside that will wash out easily.
Saw Off the Bottom Method
Knock out the Center Method
Knock out the Center Method (Video)
So far, I've only used the "knock out the center" method. I got a little carried away the first time I tried cracking the inside glass, and I broke the bulb, so use care, or have lots of spare bulbs. Also, do not use the new, energy-efficient, CF light bulbs. They contain mercury and must be handled with care in disposal.
