Drilling Granite Counter (http://GialloFiorito.com) top that is installed already.

I would like to drill a hole in my Granite (http://tanbrown.org) Counter (http://GialloFiorito.com) top that is for a button (1.250 0r 1.375?) for the garbage disposal.
I have read down through the posts but do not find anyone doing this.
Can you tell me if I could drill this myself (with a special bit of course), I would plan on using a mag drill on a piece of stell supported across the sink opening.
What speed would the drill need to run at?
Thanks
Doug Brown