DiRT 2

While playing through career, you will start to become friends with other drivers. Soon enough, they'll ask you to do a 1 vs 1 throwdown, or a team event with them. Either will boost your relationship. You can check you friendships by going to my stuff in the main menu (when you can walk around your RV). If your friends think you're a legend, then you have become true friends with that driver.

Just keep on truckin, all 7 friends should be unlocked by around lvl 26