Alright - for this cheat to work you must have a profile already made in the game. To join a certain team, find the metal.ini file under the system folder in the 4x4 evo2 Terminal Reality folder. Open it up and find the section that says

Profile = yourprofilenamehere

under that section there is a line that should say

team=none

change the none to the name of the team you want to join

ex.
team=Sakurai
team=TeamDeath
team=YoungRacing

(remember to change ALL the lines that say team=none)
save the file and play the game. Hint - don't get the team death toyota truck. really bad vehicle.