Buy some Xbox Live Gold cards or try and set up another Gold Live account...you can create free Silver Live accounts but I don't think you can play online with those accounts. So you're going to have to pay if you want more than one account.
create a new Windows live account. Then jump on your xbox, and create a new xbox account with that email. Once you have done this you should be given the option to have a free 1 month membership.
that is why when people create accounts, they always get "that name is already in use" error messages . Anyway I don't really agree with people doing that but whatever tickles your fancy I guess.