How to rebuild the Launch Services database in Mac OS X Snow Leopard
If you notice in Finder that your "Open With" menu shows duplicate applications then you may clean this up with a rebuild of the Launch Services database. You may carry this out in Mac OS X Snow Leopard by running the following from a Terminal command line: /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user