Hi sbaya,
The action of the car is knight_on_wheels. In the end theres a function call car_player(). write this function above the action and put your code there. It could look like:
Code:
function car_player()
{
  while(1)
  {
     if (key_space) c_move(me,vector(whatever),Null or sth); //check the manual for c_move
     wait(1);
  }
action knight_on_wheels()
...

i'm not exoerienced in gamestudio, so I'd be glad if some experts could correct my code a bit.

PS: please use code tags [code ] your code here [/code] (remove spaces)