I doubt Barca would still be interested in Tachi, now that they signed Van Bommel for free. And i dont think they will be interested in Trez again, because they bought Maxi Lopez, and Larsson should be back from Injury for start of next season.
Xavi is indeed a great player, however he's not that convincing defensively, so this is probably all rumors once again. Capello wants two players in the middle of the park who can tackle, and I don't think Xavi fits that description. But if we indeed have a chance to buy him we should because he's a great player, one I have always admired.