i recently upgraded my itunes but in doing so have lost all my purchases and all my playlists. i tried to 'check for available downloads' but that only gave me the last album i downloaded. i've lost almost �100 worth of downloads and all my playlists.
are you sure you've lost them or are they just no longer in Itunes?
Itunes doesn't store your music, it just catalogs them.
double click on your my documents folder on the desktop and have a look in my music for a Itunes folder, and see whats in there, if all your music is there it just needs to be added to Itunes again