Hit Esc and type in a cheat code:

IAINTSCARED               God Mode
SHOWMETHEMAZES            All Levels
INEEDTHEPOINTS            Win the Level
INEEDANEXIT               Win the Level 
HONEYISHRUNKPACMAN        Shrink PacMan 
HONEYIBLEWUPPACMAN        Blow Up PacMan 
UPCLOSEANDPERSONA         First Person View 
BEINGPACMANOVICH          First Person View 
GETALIFE                  Add 1 Life 
KILLME                    Name says it all :)
PACSTATS                  FPS and Other Stats