Searching the net I ran across this tutorial for modifying the Canon Rebel XT for astronomy use. It is a little involved but @ 90 bucks for the filter as opposed to spending 400 to modify a Rebel XT I think the work is worth it. Here it is:
I am going to do this mod to my XT soon and will hopefully soon (if life doesnt get in the way) post my results.
Disclaimer: I assume no responsibility if something happens to your camera if you decide to do this modification...please don't shoot the messenger .