For cheats in this game, use the DOS utility DEBUG.
 First backup your game to be edited, then type the 
 following from the dos prompt:
 
 ren e:dr.exe cheater.cht
 debug e:cheater.cht
 For infinate missiles, type: e37a3 90 90 90 90
 e3e71 90 90 90 90
 For invulnerability, type: e2dbc 90
 e 34ca 90 90 90 90
 e 344b 90 90 90 90
 w
 q