thanks for the feedback!
to answer a few questions...
-The edges are rough. I put on glasses and gloves and use sandpaper on them. I know using sandpaper on glass edges sounds like a bad idea but it works really well. and ive never cut myself. you want to use a really really fine grit sandpaper.
-as far as where to buy the tool, I have no idea. i borrowed my parents.
Another method that ive used is to dip a piece of string in rubbing alcohol and tie it around the bottle where you want the cut to be. Then you fill your sink with cold water and ice. You light the string on fire and once it burns off you dunk the bottle immediately in the cold water and it should break on the line where the string was tied. The fire heats a small portion of the glass really hot causing it to expand, and the quick cold water forces a quick shrinking making it snap hopefully where you want it. (sorry im getting my credential to be a science teacher)
of course this method is riskier but free. Id try it with some cheap beer bottles first and get good at it before you try your large cool alcohol bottles.
here are some more links with some info--http://www.doityourself.com/stry/makelamphttp://www.cowtown.net/mikefirth/bottle.htm