Since you have an active subscription to OneCare, created with a LiveID and the retail product key by Circuit City techs when they set up your machine, you must sign in with that same original LiveID in order to renew and provide payment information or use another retail key. Open OneCare, click on Help/About and you should see the Subscription ID. This is the LiveID for your subscription. Circuit City should have given you a sheet with this LiveID and the password to use to manage your account. If you don't have this, but can see the Subscription ID, you can contact support to have the password for this LiveID reset or you can simply uninstall OneCare when it expires and reinstall from http://onecare.live.com and then activate a new subscription with your newly created LiveID and a credit card or a new retail product key if you choose to pick up a copy of OneCare at retail (which may be cheaper for you.)
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
How to renew OneCare - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2908249&SiteID=2
How to uninstall OneCare - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=663806&SiteID=2
-steve
