It's a shame that such a good basketball game got such a lazy port-job to the Xbox 360.
Obviously the main difference between this version and the regular Xbox version is going to the in the visuals and the price. If you have an HD TV, then this game looks o.k. It will impress you in some areas and look like a PS2 game in others. If you have a regular TV, then you will be hard pressed to find a big difference here and I would recommend getting the cheaper Xbox version. Because like I said before, this is the same game.
The only other major (or minor, depending on your tastes) is the inclusion of the gamer points you get for doing the five achievements. This is widely known as the easiest game to get the full 1000 gamer points on, as you can get them all in one single game. And since you can find this game at any local Gamespot for around $10, many will pick it up for that reason alone.
If you have the regular Xbox version of this game, I wouldn't bother picking this version up. If you really want the extra 1000 gamerpoints, well then that is another story. This is a good basketball game, but it didn't really take the next step into the next generation quite yet. NBA 2K7 takes care of that, of course. If you do decide to grab this game, you will be getting the best '06 b-ball game on the market.