It happens now and then that when you control-click on a file to use the Open With contextual menu, you’ll see double entries, and even removed applications, in the list of available applicatiopns. A rebuild of the LaunchServices database is then the solution. (This also happened in Tiger.) The path to the lsregister command needed for the rebuild has changed in 10.5. As such, the following command rebuilds the database on Leopard:

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user

macosxhints.com - 10.5: Rebuild the launchservices database