How do I have no page background when logged out or registering?

[Hooper]

I would like to alter so that when you are logged out or registering, you don't have the body of the page showing but just the message box or registration forms. It's a register to view site. How would this be achieved?

When logging in, you then see the full page, forums and body background etc.. Just not when logged out or registering.

I managed to duplicate a template and reimport without the background, it's a matter of saying if logged in use this template, if logged out use this one.

Thanks
Hoop