When  you are about to be killed for the 4th time, press the left
mouse button to bring up the second player, and keep pressing the fire
button  until  you're  killed.  You  wil  appear  at the bottom of the
screen.

Or, try typing the following passwords to warp to each level:

Level 2 - mrwimpey
      3 - classics
      4 - whizzkid
      5 - gunshots
      6 - doodguyz
      7 - d.gibson