i know with the IPAC you have space for 10 buttons.  8 actual buttons, 1 start, and 1 coin.  with all of your buttons you can have X, Y, A, B, BLACK, WHITE, L, R, and then use start and coing for start and back respectively.  the L and R buttons just have switches in them like any other button, the only difference is that they have a trigger on them instead of an actual button to press.