This is coming from a source on Footballguys.com messageboard. Staff member there has an inside source with the Pats and occasionally will post good, solid info that is more often right than wrong:
Mike Vrabel traded to the Chiefs - Footballguys Forums
He says he is hearing buzz the Vrable move is part of bigger deal involving Cassel and Pats #1 which will potentially send back a 1st & 3rd to NE, with the teams also flip-flopping in a few other rounds to even out value.
Take it FWIW, but I wouldn't post this if I thought it was garbage. This guy (David Yudkin) has been spot on in lots of areas before and can be counted on for the occasional insider tid bit.
Again this is all SPECULATION, but it's a decent source.