I didn't read your second post, but I'll say what I know from my school.
You might want to look into getting a microcontroller such as an Atmel AVR development board. I have written small programs for it (it's written in C, interfaces over serial with Linux, Mac, or Windows), and it's fairly easy to program. I'd recommend similar boards for robotics, I know the main robotics prof at my school uses Atmel. The board I have was about $120. You can probably figure out which board is best by checking around robotics websites.
In terms of control, at my school we use infra-red. At school, the tiny little controllers on-board our tanks understand approximately 4 commands (speed up/slow down left/right treads) It is cheap and consumes little power. Another option is just to use a modulated wave, probably in the 2.2 - 2.4ghz range since that's the only legal frequency. Using standard WiFi is typically wasteful in terms of CPU and power, and it is usually way overkill. The idea of robotics is to implement exactly what you need, and nothing else.
In terms of movement, I'd suggest starting with something small, like wheels. At school, we used a tank with treads. If you're planning on doing autonomous agents, you're going to need to track down collision sensors or something similar, but I think that's beyond what you're trying to do. If you want something more complicated, you have to start getting into cervos (servos? I've never seen it spelled..), which are quite pricy.
Hopefully that helps a little.
