To start on any stage, patch your save file with any one of these Game Guru codes.

Start at stage 2 SWXSCXF
Start at stage 3 RVXSCXF
Start at stage 4 QUXSCXF
Start at final stage PTXSCXF

View end of game - Note 1 - OSXSCXF

Note 1: To see the end-of-game video, choose Zombietown from the map.