Rock Jewelry Drills

What drill should I use to make holes in rocks for jewelry?
I collect a lot of rocks with intentions on making them into necklaces but I have never had time. Now I do and I need to figure out how to make holes in them. I was looking at some dremels and they come in different volts. I know nothing about drills so I want to know what volt I should get.
As for dremels , just get a 120 volt one. That way you can just plug it in the wall when you want to use it. If you get a battery powered one you have to leave it on the charger and then one day it will stop working. You know how batt operated stuff is.
http://search.yahoo.com/search?p=drilling%20holes%20in%20rocks%20for%20jewerery
http://www.making-jewelry-now.com/drilling-beach-glass.html
I talking about the 300 or the 4000 that are in the link below.
They are corded and variable speed.
You may be able to find them without the accesories for less.$
It looks like the cordless ones are not variable speed.
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rlz=1T4GWYE_enUS261US261&q=dremel+tools+for+sale
01 Rock drill, M60