Originally Posted by Syrillian
CR brings up a good point.
Hole-saws are better suited for your application, but can be costly... and dangerous if care is not taken.
Was it Androo that gouged his hand something fierce...?
The Dremel will work, but it will be slow going.
A hole saw is the best, i have found tha cutting in reverse gives you a very controlled cut. As far as a drill, corded drills have more amperage thus more torque. That is not necessarily always a good thing. If you are making several cuts close together, say for rad fan holes, a overly powerful drill, if it gets hung in the cut, could deform the cutting surface, not to mention cause bodily harm. I have a Snap-On 12volt drill it works flawlessly.
On the other hand. The hole saw attatchment pictured earlier, partnered with a router (sideways)bit can also do a quick and clean job.
One more and possibly the most important when cutting on your case. Protect the finish surrounding the job. Cover the entire surface you wish to augment with masking tape. Then draw out your cuts directly onto the tape and cut through it. If you slip making a cut you are far less likely to damage the surrounding areas.