If you are having trouble getting the USB connection between your Ubuntu to Canon Rebel XTi to work, and don’t want to find a windows machine to use, you might use gphoto2 to download the photos from your camera.
Note: I’ve tried this on on my Dell Mini 10v 1011 running XUbuntu Precise release 12.04 with success
1) Check if gphoto2 is installed
~$ which gphoto2
2) Install if necessary gphoto2
~$ sudo apt-get install gphoto2
3) Turn on your digital camera, and plug it into the USB port on your computer
4) Check to make sure it shows up with the command as follows
~$ gphoto2 –auto-detect
5) Download the photos (assuming step 4 worked)
~$ gphoto2 –get-all-files
Hope this works as well for you as it did for me.