If you need a new website, you will need to create a different live email account and request a new Office Live account. This email account will become the owner of the site. If you want to manage all the Websites with one email or live account, you can add that account to your Website and grant the administration role to the account. This way you can use one log in, and you will be able to design the Websites for different domains. This is quite convinience when your customer is already the owner of the site, and you only need admin access to design the Website.
I hope this helps someone out there.