Hi Mate
You want to get a cone shaped Stepped drill. Bought one myself, very very good, perfect holes.
I have attatched a link to give you an idea of what they look like but you want one that goes from about 2mm up to about 12 mm in 1 or 2 mm incraments. I paid about £18 for mine and worth every penny.
Hope this helps.
Gav
http://www.amazon.com/exec/obidos/tg...05732?v=glance