Cheat mode:
Successfully complete the game on any difficulty setting to unlock a maze mini-game on the VMU. Successfully complete the maze-mini game to unlock a cheat on the cheat menu. To access the cheat menu, pause the game and choose the "Settings" selection, then scroll down past the "Internet" selection and choose the "Cheats" selection. Depending on what difficulty the game was completed on will depend on what cheat was unlocked. Complete the game on different difficulty settings to unlock different cheats.

Hidden Music:
To play some hidden Quake 3 music turn on the Dreamcast without a CD in or with the lid open. At the Menu choose the music option, then insert the Quake 3 disk (if you haven't already) and close teh lid. An image of the disk will appear and tracks four through nineteen will play music from the game.