Don't get too excited yet, folks (assuming you were going to at all), this is far from a done deal, but Nick Cafardo of the Globe is reporting that the Sox have at least started the process of accquiring Nationals shortstop Cristian Guzman.
Essentially, for the Red Sox to have any chance at him, the entirety of the NL as well as every team in the AL with a worse record than the Sox would have to pass up on him. Then the Nationals would have to decide whether to trade him or simply release him to the Red Sox, or pull him back if they can't work out a satisfactory deal.
Guzman is a slightly below average fielding SS with a .770 OPS. He barely ever walks, but hits well for average and has some reasonable doubles power. He is signed for $8 million through the end of 2010, making it unlikely that other contending teams like the Rays or Rangers will attempt to block them, lest the Nationals let him walk and stick them with an unexpected bill.
This move comes close on the heels of Jed Lowrie's injury, and given that Guzman is signed through 2010, it seems likely he would be the starter next year as well.