well suit your needs, like you said, you ahd a 500mA adaptor, but if this wouldnt suply the neceassaary current the i dont think that batteries would, maybe good batteries.
and i think that you might use a car battery lol
but i have some questions:
1) could you send a picture of the robot, maybe email it to me.
2)how did yiu control the robot via the computer, what port did you use, serial or paralel..?]
3)how did you connect the motors to the wheals, did you use gears and where did you get them from?
and these are the questions for now. why i am asking them is because i want to build a robot of my own.