special servos

are you sure you want servos? You might be better off with some DC motors.
you can get a whole bunch of metalic servo attachments
here
The servos I use come from here
I dont know if they make servos that will fit your requirements.

Have you considered just buying a remote controlled car and ripping it appart?
(like this )

You're right, silly me. DC Motors should do fine.
Let me check if conrad has some descent ones.
DC Motors should be compatible with a usb-controller right(just analog or are there digital ones)?

-CProgrammer

I am unaware of any DC motors which can be controlled via usb or serial. I have come accross some serial-controlled servos though.
But this is probably because DC motors are a lot easier to control, just send a voltage down one line. So the cheapo control board mentioned in the other post (http://www.zworld.com/) should work fine.
Keep in mind that if you want to attach encoders to the dc motors you will need at least 2 digital ins for each motor.

You really should try to figure out what exactly you need in terms of sensors and motors, because that will determine what controller you can end up settling for.

(so one idea, might be to use your laptop as the powerfull calculation platform, and then just use a cheaper controller to interface to your hardware)

Perhaps you should just buy one of those ultra-cheap toy cars (like $30) and rip the motors out of them and try and get the controller for that working, and then go out and buy all the other sensors&motors you need - because you will have a better idea of what you will/wont need.

Well, teh googol gave me this, which looks like a cheap way to start. Either that, or go hardcore and get yourself a single-board computer and build a custom circuit board with some FETs (or L293E stepper controllers if you want to save some space). That's actually what I'm doing at work at the moment, it's remarkably fun! :)