Couple of querstions:

Pedal_Wench: is that 13-29 Cassette an 8 or 9 speed or is it a 10 spd? Car's bike is old enough her levers are 8 or 9.

Emily - your crankset and levers are Campy, right? What rear deraillleur are you using with the Shimano XT cassette? This could be a good solution though Car's hubs are probably Campy-compatible. I think you can get a Shimano to Campy adaptor for cassettes but not vice versa. Hmm, I'm curious about the details of your drivetrain and wheels.