The alternative is to sign in at http://billing.microsoft.com to see your OneCare subscription.
If you have gone through the activation/subscribe process in OneCare, yet it remains in trial mode, that means that the subscription credentials were not returned to OneCare on the PC. This usually means that it has been blocked by something or a server error has been encountered. Make sure that you have no other active security software installed - firewalls, parental controls, antispyware, etc. - before clicking subscribe in OneCare to try and activate the installed copy with your Subscription LiveID.
If you encounter problems, please contact support.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve