Boston ownership still has to okay the deal, which would involve the BoSox paying all of Lowell's salary ($12 million in 2010).
Lowell would give the Rangers a righty bat that could play first base, third base, and DH, presumably in a David Murphy-esque 400 PA role. He's a useful part-time player, not someone you want to give 600 PAs to.
Max's star fell quite a bit last year, with wrist problems limiting him, and the Rangers not even bothering to give him a September call-up. He seemed to have plummeted in the pecking order, and the BoSox are clearly buying low on him, although if he can't stay behind the plate, it seems questionable if he'll hit enough to play every day.