There are several schematics and kits out there to build this particular piece of nostalgia, but these all have something in common: the LEDs are either on or off, and that's it.
Of course, the LEDs used in the TV series had a serious afterglow, which some schematics reproduce by using elco's -- which has the disadvantage that the LEDs are slow to light up as well.
With a microcontroller, the solution is easy: use PWM! With a 16F628A that uses it's internal oscillator, I can drive 14 LEDs -- Kitt only had seven! You know we've made some pretty cool technological progress when you can have twice as much LEDs in your scanning display as you could twenty years ago. :)
It's finished now, and the effect is very, very cool. I've used the ultrabright, narrow-angle red LEDs -- I've tried capturing a little movie to show the effect, but they're too bright for my crappy webcam. You'll have to take my word for it.
Now I have to make one for klik, with blue LEDs -- like the one in my icon.