If you've never played any Halo games before don't start here.
1. They don't have an xbox 360
and or
2.They have played Halo 2 alot and are really good and don't want to move on with all the noobs to halo 3.
group 2 is where your going to have some problems. If your a newbie starting on halo 2, Your going to be playing with some Really good people and thats why i would recommend starting with 3 because it isn't all pros. Obviously playing with people better than you can help you learn and get better. But it can be extremely frustrating at times. Halo 2 probably was your best choice for Multiplayer Gaming on the Xbox but If you are new to the series start with halo 3.