If any of those other candidates somehow slip up over the coming months, Gingrich could enter the race with an organization already built. His ability to captivate small crowds could bode well for him in the caucus environment. If he were to win Iowa, he would have the beginnings of a Nixonesque return to prominence, a la 1968.
Al Gore's entry point might come later. Suppose Obama, Clinton and perhaps Sen. John Edwards, D-North Carolina, or others split small, early primaries and caucuses among themselves. It's a not-so-well-kept secret that Florida's legislature is intent on moving that state's primary date forward to immediately follow New Hampshire's. That would cast Florida's huge shadow over other early primaries and give Gore a chance to tap into Clinton's base in the critical Palm Beach and Broward counties in South Florida. There's still plenty of sympathy for Gore from the 2000 contest, when many Democrats believed he was "robbed" of the presidency.
This would also rob Obama of the opportunity to score a big potential win in a stand-alone South Carolina primary, where the Democratic electorate is heavily African-American.
As for the general election, Newt Gingrich might seem a negative, but in the eyes of some voters, he wouldn't be nearly as negative as Hillary Clinton. Al Gore would seem to be more in touch with independent voters than, say, Mitt Romney, who is feverishly working to capture his party's right wing. Moving back to the middle following the primaries might be problematic for him.
No one is saying either of the two "G men" -- Gingrich or Gore -- will pull off a political miracle in 2008. Even so, writing off such big-time players this early is premature to the point of foolhardiness.