I thought of this when I saw the title of the thread.
Oh hey I play that game every once in a while. Is it possible to play with your buddies on that? I forget...
I don't know if that's a serious question or not..
But yes, of course you can play with your buddies on it. Are you playing it on the PC or the Xbox?
Edit: Actually, if you are talking about playing it in the same room on split screen. Then, no.. You can not do it. But, Team Fortress 2 is now free to play on PC on Steam. So as long as your friends also have a good computer, they can play it too.