With the release of the Yahoo! Application Gallery beta, the Yahoo! Music Engine team have announce they are moving their old stand-alone site for plug-ins to the Music Engine application.Plug-ins need to be re-submitted to continue to be publicly available, and the "Unofficial" plug-in site will be going away soon (although how long is not mentioned).
This post to their blog talks more about the move:
1. when Yahoo music can be played in PSP
Posted at 6:14PM on Jun 7th 2006 by Zahid Pervaiz