In order to get endless lives in this game, use the DOS utility DEBUG.
First make a backup copy of the file that you will be changing. Then type the following in dos:
ren e: \ alien.exe cheater.cht
debug e: \ cheater.cht
For infinate lives, type: e e1ae 90 90 90 90
To Stop The Timer, type: e b8be 90 90 90 90
Then rename the file CHEATER.CHT back to the original name.