To turn the Mad Monks into your slaves, use these cheats:

DOS Version:
Press Ctrl-F3 to activate monk mode
Control the monk with the T-Y-U/G-H-J/B-N-M Keys
Press TAB to switch monks

Windows version 1.2 and 1.3:
Click on the dot in the upper left corner of the main menu screen
Type CTHULU (v1.2) or YOG (v1.3)
Listen for a 'gong' sound.
Control the monk with the T-Y-U/G-H-J/B-N-M Keys
Press TAB to switch monks