Xbox Details

can you tell me the steps I take to get on xbox live 360 with multiple people on the same console on call of duty modern warfare 2. I have tried to but I just can’t seem to figure it out! Please help! Thanks!

        

I have an original Xbox. I was told you can buy the replacement part on Ebay for the red ring flashing. When I go to Ebay it only shows Xbox 360 when I do a search. I want to know if I buy this part, will it work in my regular Xbox.