You should be able to manage your folders under the "organize" tab and make sure your Media Player is set to auto-refresh. For more information about he Media Player set-up go here: http://windows.microsoft.com/en-us/windows7/Getting-started-with-Windows-Media-Player.
If I know more specifics about how far you have gotten, what you have done to set up so far I can be of more help.
I am having an issue getting media player 12 to update my library of music. I have a Windows Home Server with all of my music in the music share folder. This folder is set to the default save location in my Windows 7 machine's music library.
I know with older versions of media player you could force a refresh of the library but i can't seem to find it in 12.
Any help would be great