There appears to be no clean way to close/reset locks on files accessed through Samba shares. I've had situations where a user cannot open a file for editing as it is reported as being already open (often by the same user). smbstatus shows the file lock and pid, but the pid appears to be specific to the client host. If that host has multiple users (i.e. a terminal server) then I cannot kill that pid to release the lock without causing other problems.
NT 4's Server Manager lists open resources on a server and allows you to close them. It would be nice if Samba allowed you to remove specific locks when you were sure (or fairly sure at least!) that these were no longer in use, but due to some problem, you were prevented from editing the file.