I infer that it basically means that the construction you have is a Lego set with some of its moving parts motorized by NXT motors and controlled by a NXT Intelligent Brick. And that is what I did again here.....I tried to build something like the somewhat new Lego Technic set "Buggy," and then changed it to put NXT elements inside of it. I got the instructions for the set on the Lego website, and then tried to build a version of it, which was a challenging because I didn't have all 
of the right parts, especially parts that operated the front suspension and steering. I had to use an extensive construction of pieces, the inspiration for which I got from this project. However, it turned out all right, you can see it in the first picture. Then, I did with it what I built it for in the first place: I put the NXT inside of it. You can see the result in the second picture. Although the NXT Intelligent Brick may look a bit "raised up," I am rather happy with the result. One motor 
drives it, the other steers. You can see an overview of the drive and steering mechanisms in the third picture. The motor on the left in the picture turns the differential and the motor on the right in the picture goes into the 90-degree motion change that you can see (I am happy that there is no gear slippage when the front steering is not encountering much resistance, but there is some with resistance), which then ran down a central shaft to where it goes through more gears and eventually, to the rack and pinion steering system. The other side of the differential is connected to a mechanism (in the current buggy, I replaced the two darker gray knob gears to a larger and a smaller gear) which operates the pistons on the fake "engine" quite like in the original set. The original set had no differential, the "engine" was one stud lower and the gearing was different. The construction the rear differential is set up on moves up on down on the two motor's axles and a suspension piece about the same position it was in in the original set gives it a bit of back suspension. It also has independent front suspension as well as front wheel steering through the two front wheel setups.Nato
