Press Tab to enter the map screen. Hold Ctrl and type CFODDER 
exit the map and press Return to jump to the next level.

Steve Hartman

When you are playing, go to to the map, hold Ctrl and type Fodder. Then get out of the map and press Enter. you will skip a level. (note: you don't have to go to the map each time and type the cheat, all you need to do is press enter each time)

Jonathan Kornik

Click load icon then hold down both mouse buttons for a few seconds and release. A screen will appear with hard-man option and level select.