You must type "gabbi" (without the quotation marks) while holding the Ctrl-key down, before entering any other codes (or "iguana", if you're running a version prior to v1.6). After a successful entry you should see two yellow lines of text appear in the lower left hand corner of the screen, saying "Cheat level two reached" and "History log updated". If it doesn't work the first time, try typing it a bit faster or a bit slower. Also note that the cheats won't work in the 2004 remake of Jagged Alliance 2 (JA2: Wildfire).