you need 2 profiles with different xbox live accounts on 1 xbox 360 you need 2 profiles with different xbox live accounts on 1 xbox 360
you can if you play coop campaign mode. The second player will be the arbiter
yes
It will be, yes.
Yes, if you have the Halo 3 PC version of the game
They stoped online play for Halo 2 back in June 2010. And you need Xbox LIVE to play halo 3, however on the new Xbox 360 u can play halo3 online for free
you play online
yes you can
some might get bored of halo and play w.o.w, but only if they don't have online halo 3. they also get bored of w.o.w and start playing halo 3 online.
No, halo 3 forge is not offline, you may play it online with friends or others.
no
Yes it is two player on the same console and 4 if over xbox live
You could get on a LAN with your friends