welcome to the XTi club OMEGA
I have one also but with the Sigma version of that lense (70-300 F4-5.6 APO DG Macro)
You definatly wont be dissapointed with your decision
Ive had mine since the end of september and absolutly love it.
You can see some of my shots here to kinda get an idea of what ive been able to do with it so far, the hockey and car shots are all taken with the Tamron 28-75 2.8 though, but the rest is all with the sigma lense (which is almost exactly the same quality of your 75-300.
here's the link if you want a look:
http://www.flickr.com/photos/mb-photography/
Oh, and here is one of THE best Canon forums out there, you should DEFINATLY check this out if you havnt before, TONS of info and help (and examples):
http://photography-on-the.net/forum/index.php
Enjoy!
-Mike