Ah. I am currently in the process of doing this. Have a read:
http://www.singletrackworld.com/forum/topic/stripping-paint-off-an-alu-frame-any-tips
The best advice I can give you, from the knowledge and experience I have now gained as a result of my endeavours, is:
Get someone else to do it!
Seriously though, if your paint is anywhere near as tough as the powdercoat on my frame, it will take bloody ages. Quite therapeutic mind, and I’m sure it’ll be extremely satisfying once it’s done.
If having it done professionally, make sure they either strip it chemically, or using a softer blasting medium like soda, as other stuff can damage aluminium. Take it to a good place that knows how to do alu bike frames.