D12 will be appearing on two tracks from Eminem's upcomming hits album "Curtain Call".. Mr. Porter and Proof rap on the single "How Come" and the whole D12 band sings "Purple Pills", There is a 100% of probability that Dr.Dre will appear on some tracks, and there isn't still a confirmation if any Shadyrecords member can have a verse on the album. Dido will be singing the hook on the "Stan" track.
Obie Trice says a little intro on the "without me" track and Frogg on the "Just Don't Give A Fuck" track.
Eminem will come up with two new tracks: "When I'm Gone" and "Lucky Transition"... And one Paul skit is expected to appear on the tracklist.
Curtains Up and Courtains down will form part of a track each: probably the track 1 will be "Curtains Up / Lose Yourself", and track 22 will be "When I'm Gone" Eminem & Dr.Dre will handle the entire production.
EDITED sorry, posetd this a week ago so I forgot to post the source: http://www.vh1.com