Silver (Free) memberships cannot play on Live. They have free weekends every now and then, but if you want to play Black Ops online you'll need to purchase a Gold Membership. Did you just get your 360? You receive a free
month of Live when you first create an account.
Yeah, if you create a new profile( you may have to create a new email on microsoft) and then get on the xbox. Somewhere on your dashboard it will say " Join Xbox Live" There you will continue to sign on with the new email somewhere down the line it will
give you the option to get a gold membership free for a month.