You would need a metal bit for the dremel.
Here is a standard type circle cutter for about the same money.
http://www.epinions.com/prices/Gener..._Circle_Cutter
You will probably trash out the bit doing metal but it would probably last for a few holes. Score one side then flip the work over and cut. Make sure the metal is clamped down
because sheet metal has a tendancy to grab in a drill press.