Hi Ken, thanks very much for your reply. Now it's all much clearer. So, if I understand correctly, to power up 4 DC motors and use I2C I need the processor board, a prototyping board (any would do for I2C) and the motor shield. The USB/ICP one can be removed after flashing up the code and powering down the system, can't it? (assuming I don't need to change the control software any longer).
Thanks again.