Vieira's the best DM in the world, in my opinion. He's a real driving force for Arsenal and Zidane's admitted that he loves the freedom he gets playing for France because he knows that Vieira picks up anything he drops.
About two years ago, he looked like leaving Arsenal, as he felt it lacked the ambition to win trophies. They've since become a lot better, with Henry in particular maturing to become a world class player, and they finally look like a tema that could suceed in Europe. I don't think he's eager to leave anymore, and Arsenal are certainly unlikely to sell for anything less than a stupid bid of the Real Madrid ilk - money Juve just won't pay.
Vieira didn't enjoy his time at Milan, and he's unlikely to be willing to return to Italy. All in all, I don't see him joining Juve.