The thing with Canon is that if you loose the CD that came with the camera or you bought a second hand camera without the CD, they don’t give you the option to download the software again from their site. Apart from the drivers you cannot download things like EOS Utility (very useful for intervalometer), Digital Photo Professional, etc.
Anyway there is workaround for this
Go to the official Canon Drivers Site and after you find the model of your camera choose to download the version that corresponds to your MAC OS
When the download finishes, extract the file, run the .dmg file and the application installation starts.
Copy the .app to desktop or somewhere else and the right click and choose Show Package Contents
Browse to Contents -> Resources
and delete file Info.datx
Then run again the .app installer and check that the software installs from the beginning
This was tested on a Canon 40D and Canon 5d with Mac OS 10.7 (Lion)