HexCheat:

 If you want to play the higher missions of this game, but you do
 not have the potential to survive the lower levels, here is a way
 to activate all levels.

 Load the file options.cfg into the hex editor and change the first
 two columns to:

 0000000  32 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 0000010  00 00 00 00 00 00 01 01 01 01 01 01 01 01 01 01

 Now you can select every level you want to.