It's perfectly legal. To see what wildstang did, I suggest you consult their web-site and view their flash video.
http://www2.wildstang.org/2003/video...SOverview.html
Essentially, it requires reading in variables from various sensors and then reacting to them autonomously. The difficulty level of doing this depends on what you decide to do. Some teams have spent thousands of man hours on this, tried, and failed, some teams just read wheel counts so they know their speed. What you do depends on what you can handle. Its not a small task to make something completely responsive, but various levels leading up to completely responsive can be done.
A simple idea of how to react to it autonomously, take a look at this "basicified" code.
Wheelcount = sensorreadin
If wheelcount > 50 then slowdown else speedup
end if
slowdown:
speedup: