Halo 3 co-op joining over xbox live?

[William B]

How do I play halo 3 co-op with someone over xbox live? Is it like gears of war where anyone joins, or do I have to invite someone or be invited?

 

[Person]

Just choose someone off of your friends list.

 

[some dude]

If they are your friend, then they click friends from the guide, and have the option to JOIN party. If not a friend, you can invite them. There are different options but that is standard!

 

[some guy]

first you have to go to the campaign lobby (no the solo) and then press y to bring up your friends list, and then you can select one of your friend to join you by sending an invite.