Mondo Technology has a PIC microcontroller circuit for running your Dremel at slower speeds.

“The Dremel drill fitted with a mini drill-chuck on a stand is a great setup for drilling circuit boards. The problem is that it does not do low speeds very well. My unit had a failed internal speed controller, so I just wired around it and connected it to a regulated 24 volt DC supply. This worked OK, but I would like a slower speed when drilling boards. Slowing down with a lower voltage, however, causes it to stall out completly when it begins drilling. What I needed was a circuit to actually increase power to the motor under increasing load.”