Trekdude,

I was afraid you'd say that, aluminum frames are unique beasts in that they are heat treated to relieve any stress cause during welding. Assuming of course your frame is welded. It may be a bonded frame which it might be easier to repair. Either way your going to need to find a competent repair shop to do the work, and it won't be cheap to have it done as your frame will more than likely need to come apart. After which it would need to be reheat treated if it's welded. The only other thing I can think of would be to drill a small hole in the bottom shell into the down tube and push out the dent from inside the tube. But even that is a lot of work, how bad does the dent bother you? Does it affect the overall stiffness or ride quality of the frame? Is your bike still safe to ride?

BTW I'm not a frame builder I'm just a guy who happens to do metal work as a hobby. I'm sure there are other people on here that are much more capable than I at helping you with your problem.

Good luck!

Cya,

jr