Open OneCare, click Help/About...
Your subscription ID should be visible there.
Sign in at http://billing.microsoft.com with that LiveID and update your information.
If the subscription ID is not listed and you are unable to log into the Billing site to see your OneCare subscription listed, please contact support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve