damn you for bumping this!!
taken from the opk's readme this will get you started:
Standard in-game MAME controls:
D-Pad and Analog Pad: UP, DOWN, LEFT and RIGHT
Buttons: A,B,X,Y,L,R
MAME Buttons: 1,2,3,4,5,6
Button SELECT: Insert credit
Button START: Start game
Buttons START+SELECT : Mame menu. The "MAME menu" can be used to Redefine DEFAULT keys for all games (use B button)
Buttons START+L+R: Esc (exit to mame frontend)
Buttons L+R: Pause
Buttons SELECT+R: Show FPS
Buttons START+L: Show profiler
Buttons L+B: Snapshot