some big problems.........

hi i am making a car racing game and i need help from you.The problems are
:-how do i count points and how do i use it to activate the finish line so that when a player have collected the given then he allowed to go in the next level

:-the other (big) problem is that i don"t know how to make opponents for this game
if any one know how to do solved these problems please help me.

http://blenderartists.org/forum/showthread.php?t=113095

and you could try to make something similar for the checkpoints