Just like you said, YAMMM stores .xml files that stores the meta data for the files. All YAMMM and My Movies does is store the meta data into the folder of the movie.
If the only issue you are having is the meta data not showing up on another pc, it could be the database could be corrupted on the pc.
Delete and rapair the media database: http://www.softwaretipsandtricks.com/windowsxp/articles/117/1/Delete%7B47%7DRepair-the-Windows-Media-Player-Library
try that and see if that works first.
-Josh
