If you start listing all the features that can be used for robotic purposes you'll find that it is cheaper to buy a netbook than buying LCD, wifi and bluetooth modules, cameras, speech synthesizer modules, keypads, memory card readers, speakers and many other stuff.
Thats why I decided to make this platform to my netbook. To let the computer control the motors, I tried two different ways: Firstly I used a arduino duemilanove with two motor driver boards , but then I found that it would be much easier if I just used a motoruino .
With this I could create lots of different applications that let my computer follow certain colors, follow human faces, detect flames, drive around the house avoiding walls, be remote controlled through the internet or using a wiimote, and the list of possibilities is almost endless.
You can learn more and download it at its page: http://www.franciscodias.net/applications/openframeworks/computer-on-wheels-controller
Or, if you prefer processing, you can find and download some examples that I've already done at my website: http://www.franciscodias.net/processing-applications