Canon has posted some updates for their photographic software on the Canon USA website:
EOS Utility 2.4 According to the release notes EOS Utility now fully supports Mac OS X 10.5 so every Canon user with Leopard should grab this download. It now supports the EOS Kiss X2/EOS DIGITAL REBEL XSi/EOS DIGITAL 450D and it fixes a Remote Shooting problem too.
Digital Photo Professional 3.4.1 Digital Photo Professional now fully supports Mac OS X 10.5 too. DPP now incorporates a new luminance noise reduction function for TIFF/JPEG image and it adds support for the aberration correction function on sixteen more lenses and also some extenders.
Picture Style Editor 1.3 Was updated for compatibility to Mac OS X 10.5 too and now supports the EOS Kiss X2/EOS DIGITAL REBEL XSi/EOS DIGITAL 450D
You can find some more improvements and fixes in the release notes on the download pages of every file. To download these updates you can follow this link which will bring you to the driver downloads page of the Digital Rebel XT. You can grab the files from there regardless if you have a different EOS DSLR. Just select your OS from the dropdown menu and click on the updates.