Really if they could keep Jaimison, I don't think he hurts the team at all. Walker has to go, and they have to get a scrappy, defensive center, because everyone knows that Dirk offers nothing defensively despite his size.
The way I look at it is that there are two kind of centers, one that is just a purely dominant big man who overpowers and is, well, dominant (Shaq, Duncan) or else the center that acts as the sidekick to the power forward, doesn't do a tonn on offense or defense, but is a big presence in the paint and can distribute the ball well and score/rebound when the time comes, the best example of this is Vlade Divac, but guys like Ervin Johnson fit this catagory also. In my opinion, if you don't fit into one of those catagories, you aren't a very effective center (maybe a few exceptions).
Now Dallas is in a predicament. They don't need another roleplayer to fit in the holes, but they don't have room offensively for another dominant big man. Dirk offers nothing when it comes to getting strong rebounds, and that is exactly what they need. The best guys for the job would be Ben Wallace, Brad Miller, Erick Dampier, Dennis Rodman
So basically they probably won't have any luck in this offseason getting the big rebounding center that they need.