One disc is for SP and the other for MP. It isn't really that bad, just put in the disc you want for the version you are playing. I think its kinda cool, once I am done with SP, I can uninstall and not worry about it.
My 360 isn't allowing me to install 2nd disc (campaign) what am I doing wrong?
Instal both Disc 1 and 2 from the Dashboard. Play either an DL the Update. Then go to the In-Game Menu (it will prompt you automatically) to Instal the HD Texture from the Game itself. That will be 3 Installs total with one Update.
It has always been like that since they came out with the install game to hard drive. You must have the disc in the Xbox to verify you actually have the game, otherwise people could just install it onto their hard drives and then sell the disc itself but
still play the game...