Can't get WMP11 to load albums from flash drive.?

On my WinXP system, using Windows Media Player; I have a lot of music I riped to my flash drive however I have other songs I transfered from an older computer. MP only recognizes the albums I riped recently. The other transfered files are ignored. I can select the files and drop them on the Play List edit area and the song will play just fine. I just can't get the album or song to show up in the Library. Anyone know how WMP stores the library and if I can edit it directly, or if there is a way to force WMP to accept a new album? I've tried "Add to Library" and selected the with no luck.