It should have worked with 300D, 400D, 450D too, but I have only Rebel XSi--450D--for testing =)
I put 2 buttons in there, 2s-delay-shoot, and immediate shoot. However, I found that 2 seconds delay shoot is much better since it will show LED when pressing. Much easier with the feedback. The range with Palm TX is around 10ft (3m) which is acceptable.
Here you go :-) At least it can save some $$ on real remote, and it's fun to use.