This cheat will allow you to select any level for any tribe. Go to each corner of the menu screen, starting at the top left and go in a clockwise direction, and press BOTH mouse buttons each time until you hear a lemming faintly squeal "Let's Go". You should hear this at each point of pressing the mouse buttons. Now you can select any level on any tribe and have 60 lemmings on each, which means that you only have to complete the last level of each tribe to complete the game. But you still need to complete every level to receive the talisman.