Database Rebuild?

I just synch’d 1028 files onto a 4GB PNY external card (using about half the space). It took a while to build the database, but it doesn’t find all the songs. How can I perform a rebuild that will find everything on the card?

The Express seems to be limited to keeping track of only 1000 songs.  Also, if they aren’t tagged properly, they will show up as “Unknown”.