Actually, Sharpton as a third party candidate is the best thing that could happen to the dems in 2004. The presidency, barring unforseen catastrophe, is Bush's in 2004. The big danger to the dems is their base will be depressed and that will elect lots of Repub senators.
Sharpton as a third party will turn out the black vote in huge numbers. They may vote for the Rev at the top of the ticket. But they will pull the lever for RATS for senate.
Somehow I don't think the party higher-ups would look at a Sharpton third-party run as the best thing that could happen to them!