It's possible but very farfetched. The House will of course vote for Bush, and the Senate, if everyone votes on Party Lines, will vote for Cheney. With Zell Miller crossing the lines, it makes it that much less likely that the Democrats could win. Even if the Democrats manages to get a couple of Republicans to vote with them for Edwards, the tie would be broken by Cheney himself. The likelihood of Democrats pulling even that much off is slim, since these votes are not secret and the dissenting Republicans would be open to recriminations from the party.

Basically, if it is a tie, Bush/Cheney will win.