What I am about to say may sound crazy, but I think that the only rational thing for Harold Ford, Jr. to do is declare that he will indeed run for reelection to the House while simultaneously seeking the Senate seat. Ford can't afford having Cohen on the general-election ballot potentially depressing black turnout and otherwise creating an upheaval in Memphis when every man, woman and child there needs to be working for his Senate win if he's to have any chance at all. He might take some lumps for not being "confident enough" to leave his House seat, but he can claim that he was asked by his constituents to run for reelection so as to eliminate the possibility of a divisive House primary tht might hurt the Democrats in the gubernatorial and Senate races, while still having the intention of winning the Senate race and serving all of the people of Tennessee. He could also promise to announce his resignation from the House, effective January 3, 2007, the moment that he is certified as the winner of the Senate race, allowing time for a special primary in late November and a special general in mid-December so that the new Congressman may be sworn in on January 3 with the rest of Congress. (How are special elections run in TN, DJ? Does everyone run in one ballot and the top-two guys (regardless of party) go on to the run-off if no one gets 50% (as is the case in some states that don't otherwise have a run-off)? If that's the case, then a special election would reduce the odds of Cohen being elected to the House, since the general would likely feature two Democrats, Cohen and a black guy.)
As for the legality of Ford running for both races simultaneously, I'm sure that TN law prohibits him being on both ballots simultaneously, but I believe such a restriction violates the U.S. Constitution. When states passed term-limit laws for Senators and Representatives, the laws did not say that the person could not be elected to more than X terms (which even the states knew would be unconstitutional), bu that the person *could not appear on the ballot* for more than X terms. The Supreme Court ruled that states could not add qualifications for Senators and Representatives beyond those contained in the Constitution (age, residency, years of citizenship), and that denying candidates access to the ballot because of an extra-constitutional qualification violated the Constitution. So if I were Harold Ford, Jr., I would file to run for reelection.
Remember, while a person may not be able to serve simultaneously as Senator or Representative, it's far different to deny him the opportunity to run for both offices and then deciding where to serve. If a sitting Senator who is not up for reelection runs for the House, he can decide if he wins which seat he'll keep; running for both seats would be the same thing.
Firstly, Junior is already committed to running for the Senate, so his running for the House as well is out (as far as I understand, you can run for multiple offices at the same time in TN, so I believe he could run for both, but I'm unclear as to whether he could be NOMINATED for more than one office at the same time. John Jay Hooker does this in every election, often running for multiple nominations).
However, if he did run and win both the House and Senate races at the same time, setting up a special election, you'd still have the exact same situation we have now... a total free-for-all on the Democrat side with the likely recipient being Sen. Cohen, the strongest White candidate, and a very fractured situation amongst Black candidates. There has not been a special election in TN for a Congressional seat since here in the 5th when Bill Boner vacated to become Nashville Mayor in 1987. Each party holds a special primary (of course, all the action being on the Dem side), and you could get nominated as long as you got 1 more vote than your opponent. The '87 special primary featured 3 main players, Bob Clement, who had moved into the district after 5 years earlier nearly winning the GOP 7th district against Scumquist; Phil Bredesen, then a business exec just on the heels of a loss to Boner for Mayor; and Jane Eskind, a former Yankee liberal RINO carpetbagger-turned-'Rat who had been a political fixture and candidate for office since the '70s. Eskind and Bredesen spent over a million each destroying one another, allowing Clement (ostensibly the most Conservative of the bunch) to sneak past Bredesen, winning a surprising 40%. Clement easily won over a Republican businessman in the early '88 special-general.
In any event, as you can see, Ford would only serve to delay the inevitable primary mess that will probably see Cohen win (and, Ford's stunt would also cost the state taxpayers a fortune to fund that primary - which would really make him look bad were he to try it, you see how that "hedging your bets" stunt worked for Lieberman in '00, who realized he probably wasn't going to win for VP but didn't want to be out the Senate seat, which might've helped booster the GOP ticket).
The real interesting event will be in '08, because unless Cohen somehow becomes canonized within the Black community in the interim, Junior might try to come back and get his seat (or if he doesn't, another group of Black pols fighting one another). If Cohen can get to 35-40% in a fractured field this year and in '08 (in the absence of Junior or Junior and a lot of others), he is golden. Another interesting thing, if Cohen vacates his state Senate seat mid-term, take a guess which party gets to appoint his successor ? Having a White Republican in Auntie Ophelia's seat and perhaps even a Black Republican in Cohen's would just be like pennies from heaven. ;-D