Update (6/26/2009): Imam Zaid Shakir has confirmed he is a Muslim saying this:
A good friend who is a reliable source of information called and said that Michael had become Muslim. He had been working on an album with the well-known Muslim musician, Dawud Warsby, and another Muslim performer, and the two, sensing Michael’s troubled and depressed state had invited him to Islam. He accepted their invitation. Michael was no stranger to the religion, having been exposed to it by his brother Jermaine, who had converted to the faith in 1989.
That’s what I read on this site and the Jews say the same:
Well if it’s true, then Alhamdulillah, inshaAllah he’ll change and become a better human being. If it’s not true, then he’s not a muslim.