I think he will definately be staying with Milan at least until the end of the season. He hasn't whined about the lack of playing time like some other players have done and is content to sit on the bench for now. However, if Milan recieved a significant offer I think they would let him go considering they got him for free. But Tomasson makes a good wage and that may lesson his appeal to English clubs.
The fact that he played poorly when he was at newcastle will also put most teams off. 3 goals in 27 games or so he scored. It's not the type of record that's gonna get people intrested in you.
He is a very good player, however, and I would like to see him get more playing time. I think if he gets more time on the pitch he will score some goals. I don't understand why he doesn't get subbed in more often. For example, in the game against Bologna, he was subbed in in the 91st minute. Why couldn't he have been subbed in earlier? There have been plenty of situations this year when he could have been subbed in but for some reason he wasn't.