While you could clear the various LaunchServices databases by deleting files, I prefer to use a more targeted command line tool when possible. My assumption is that the command line tool is canonical and will therefore produce more reliable results.
In Mac OS X Tiger, you could clear the LaunchServices database using the following “lsregister” command:
$ /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/LaunchServices.framework/
Versions/Current/Support/lsregister -kill -r -domain system -domain local -domain user
But, in Leopard, the LaunchServices framework’s path has moved; it is now in the CoreServices framework bundle. You can find it with the “find” command:
$ find /System -name lsregister -type f -print 2>/dev/null
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/
Versions/A/Support/lsregister
Once you find it, you can get the usage statement for the “lsregister” command in Leopard, which will at least tell you what options it has:
$ /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/
Versions/A/Support/lsregister
lsregister: [OPTIONS] [ ... ]
[ -apps [,domain]... ]
[ -libs [,domain]... ]
[ -all [,domain]... ]
Paths are searched for applications to register with the Launch Service database.
Valid domains are "system", "local", "network" and "user". Domains can also
be specified using only the first letter.
-kill Reset the Launch Services database before doing anything else
-seed If database isn't seeded, scan default locations for applications and libraries to register
-lint Print information about plist errors while registering bundles
-convert Register apps found in older LS database files
-lazy n Sleep for n seconds before registering/scanning
-r Recursive directory scan, do not recurse into packages or invisible directories
-R Recursive directory scan, descending into packages and invisible directories
-f force-update registration even if mod date is unchanged
-u unregister instead of register
-v Display progress information
-dump Display full database contents after registration
-h Display this help
Note that if you’re having Launch Services-related problems in one user account but not another, you’ll likely want to start with the “user” domain. (It pays to understand the domain structure of Mac OS X, so that you only make changes where you need to.)