During gameplay, hold down TAB and hit the page-up key
simultaneously. Then let go and press the letter P.
At the bottom of the screen it will say "cheat enabled."
This will make you indestructible. This won't help on
missions where you have to keep other things, like the
War Drum, from blowing up, but it will help in those
nightmarish combat situations.
Cameron Lewis, Editor
ZENtropy! Electronics Reviews
Or you may try this alternate cheat:
goto offset 00000358
change that byte to 32 hexdecimal
save & exit.
You can now choose any mission you want.