Also found this on the Namco arcade website.
"WANNA PLAY PAC-MAN? At the select screen input up, up, up, down, down, down, left, right, left, right, left, start. (Please note, this code works ONLY on this arcade model of the game, and does not work on individual Ms. Pac-Man or Galaga machines.)"
Maybe everybody knew that, but I didn't.