I moved your post from the off topic folder to the Install and Activate forum.
If you purchased a subscription online and have not yet installed OneCare, install the trial from
http://onecare.live.com Then open OneCare, click subscribe and sign in with the LiveID used to purchase your subscription. Your subscription will be recognized and the installed trial copy will activate and assocaite with your LiveID as the subscription ID.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator