The NXT is a Lego Micro Proscesor that can be connected to three motors* and four sensors*. It can be Programmed in several different Programming Languages, and use several third party sensors other than the four supplyed in the base set.
The NXT is not realy a "Model for robotics" it is a very functional robot disign system, which has been steryotyped to seem like a toy.
any more questions may be asked a forums.nxtasy.org where people that have a better answer will answer to you.