lsregister is a useful command line tool for helping you manager the Launch Services database.
The man page is available here. [man lsregister]
It can be found (in Tiger) at
$ /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/Current/Support/lsregister
You can explicitly register your application by specifying the -f flag to lsregister.
lsregister -f MyApp.app
lsregister allows you to log the entire Launch Services database.
lsregister -dump > ~/lsdump.txt
[How to rebuild the LaunchServices database.]
Use with caution. This will completely remove all entries from the Launch Services database. This command should never be given to end users and is only for developers.
lsregister -kill -r -domain local -domain system -domain user