Extreme-G cheats and cheat codes for Nintendo 64

Go to "Contest" mode, after at the bike selection screen, hit R,
then enter the following case-sensitive names:
Note: If the codes are accepted, you should hear a sound.

Enable magnification mode: Enter "magnify"
Enable slippery track: Enter "banana"
Enable transparent track: Enter "ghostly" 
Enable turbo mode: Enter "xtreme"
Enable wireframe mode: Enter "wired"
Fergus shot 'em up mode: Enter "FERGUS"
Fish-eye lens: Enter "fisheye"
Invisible: Enter "stealth"
Maximum weapons: Enter "arsenal"
Moon gravity: Enter "antigrav"
No textures: Enter "uglymode"
Quick race completion: Enter "RA50"
Unlimited nitros: Enter "nitroid"
Unlock Boulder race: Enter "roller"

Game developers on the bikes: Enter "XGTEAM"
Then, return to the name entry screen and enter any of the game programmers 
first names from the credits. Here are some: Andy, Craig, Darren, Greg, 
Joe, John, Justin, Lloyd, Sadie, Simon, Omri


Unlock Roach bike:
Enter "51GG95 as a password or
Finish the Meltdown circuit in intermediate difficulty mode

Unlock Neon bike:
Enter "61GGB5" as a password
or
Finish the Meltdown circuit in expert mode

Unlock Bonus track
Enter "81GGD5" as a password.
or
Finish the Meltdown circuit in extreme mode