For invulnerability in this game, use the DOS utility DEBUG.
First backup your game to be edited, then type the following
from the DOS prompt: (VGA game cheat only!)
ren cfs.exe cheater.cht
e 3efa eb 07
e 3f0f 90 90 90 90 90 eb 1d
e 3fd6 c3
Then rename CHEATER.CHT back to its previous name.