You have to use the random block, with its wires connected to the duration of the motors.
The NXT is better because it is an updated version of the RCX. It comes with three motors and all-new sensors. Rcx is getting harder to use and thwe new NXT is much easier to use.
Most robots are software controlled and hence just about any robot involves programming. If you are a beginner here are some options: 1) Lego Mindstorms with just lego parts. It comes with a brain named NXT. 2) You can also use NXT with a Tertrix kit
You can for the latest version
First, you build the robot so that it looks like it can do what you want it to do. Next you connect the "Brain Brick" to all of the motors. Then, you program it to do what you want. Then, test and then re-program it if it doesn't work.
nxt comes on syfy at 10:00 on tuesdays like ecw use to
T-Rex or T-rex
T. rex
If you already search : how to make a nxt race car you could also use some info from http://www.nxtprograms.com/MTV/drive_wheels/steps.html or can make it like this
use Lego mindstorms /NXT. Downside:VERY expensive
Tb Rex
Alpha is the first letter of the Greek alphabet.