to rotate a game, in advmame.rc do something like:
pacman/display_ror yes
or
pacman/display_rol yes
whichever is right for you.
Be careful! monitors hold charges even after unplugged! having said that, to flip your screen permanently you will need to do a "yoke flip" which is simply changing the 4wire connector from the yoke to a different set of pins if they exist or cutting the connector in two, flip both sets around, and plug back in. Do a search on it, you will most likely find some instructions...if not I will post a pic of what I am referring to tonight.