The plan i heard - which, like everything else, is a rumor - is that by 2013ish we should be up and running, maybe get the initial planes by 2008 or earlier. P-3ers would transition, just as F-14D guys are moving to F/A-18F's.
Boeing has claimed that they can have the first P-7 off the produciton line in 6 months, which i could believe. They already make the 737, all they'd have to do is shoehorn in the bomb bay and sono chutes. Beyond that, even the hard points wouldn't be much of a major design change. Boeing needs this contract bad too, they've lost a lot of big defense contracts over the last few years. They lost the Commanche just a few weeks ago.
Of course, a P-3 airframe with C-130J engines, modern avionics, and a new tactical computer would rule, just because the P-3 looks so damn badass!