The only way you'd see Kobe in a Mavs uniform would be for them to offer up Dirk straight up and even then the Lakers aren't going to make that deal. They won't trade him away unless it is a fucking steal of a deal because you aren't going to get equal value no matter what. The only team that has a realistic shot is the Bulls with them offering up Ben Gordon, Luol Deng, and Andres Nocioni. Even with that deal, I doubt the Bulls would go for that.
Even if for some wild and wacky way this trade got pulled off the only thing Dallas would get in return is a better "talent," not a better "player." Kobe has way too much baggage with his whole rape trial and the fact that the guy wants to take 30 shots a game. Dirk is highly marketable in the Dallas area and I really don't think Dallas fans would welcome that type of trade.
The Mavs don't need to be looking at trading away their cornerstone of their franchise. They need to look at where they are weak (Point-Guard and Center) and focus on those areas through Free-Agency and the Draft.
Dallas has at least two options when it comes to the Point-Guard position in this coming off-season, either try to beat out Detroit and over-pay for Chauncey Billups or try to trade for Jason Kidd. Other than that, they are wasting their time and trying to use a band-aid on a bullet wound. The Center position could possibly wait due to Diop's maturing, but its definately an area of concern that does need to be addressed in some form or fashion.