In case you missed the last several group plays, the way it works is everyone plays offline on their own, since TR3 doesn't have actual online or co-op play. Then we meet at the message board and share our progress, impressions, fun and frustrating things that happened, screenshots, video, or whatever else we feel like posting. There are no rules except to be courteous to the other players and to try and have fun. :)
So far we've done TR1, 2, Anniversary and Lara Croft and the Guardian of Light, and launched a Tomb Raider Level Editor beginner's group. There's more info in the various "group play" posts here on the blog.
Please join us and help spread the word if you know other players who might be interested.