To have mediabrowser fetch it's own metadata you'll need to have your collection sorted like mb needs to be able to understand what it is looking at.
That means every movie will need to be in a folder of it's own named EXACTLY as the movie is named, and same for the movie it's self, named exactly as the movie is.
ie D:\Movies\Cars\Cars.avi
D:\Movies\Avatar\Avatar.mkv
TV shows also need to be sorted just so for mb to fetch info.
F:\TV Shows\Lost\Season 1\Lost 01x01 - Pilot.avi
or s01e01
but the names MUST be perfect, or mb will not know what it's looking at and fetch nothing.
you must also ensure that fetching metadata is enabled in the mb config options.
to learn all about what makes mb tick check out the MB Knowledge Base or (KB),
Media Browser Community Tracker