TMZ are renowned for breaking this sort of story first, so it's not surprising that the news organisations are taking the rumours seriously.
It's odd that none of his entourage have made a statement denying that he has died; but then again, if I was seriously ill in hospital I doubt I would necessarily be concerned about premature reports of my death.
Fox News says "Michael Jackson Rushed To UCLA Medical Center" with CNN saying "Michael Jackson Hospitalised". Although it's rumoured that he's dead, I reckon any official line will be announced in the next hour or so.
Don't know to be honest. BBC News Channel is currently on the phone to Uri Geller, he says that he only knows what the news channels/agencies know. According to the BBC, the Los Angeles Times has said that he's in a coma. It's just a case of rumours at the moment.