Activating online is optional.
Simply uninstall your current expired OneCare.
Then install the trial from http://onecare.live.com and activate from within OneCare. You may want to use a new LiveID to activate. Note that the CD you purchased will still go online to get the latest bits, hence the reason to simply install the latest from the site. When subscribing from inside OneCare, choose the option to use a key to activate.
-steve
Microsoft MVP Windows Live / Windows Live OneCare, Live Mesh, & MS Security Essentials Forums Moderator