If your PC meets the minimum specifications for OneCare, don't bother using the CD. Go to
http://onecare.live.com and download and install the trial. After installation, click the subscribe link and activate your new subscription by signing in with a LiveiD and selecting the option to activate with a key. Use the product key from inside the retail package.
http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
See this post for the KB article to troubleshoot install problems - http://social.microsoft.com/forums/en-US/onecareinstallandactivate/thread/ba26b781-da18-4ce4-be8c-22647bd5d8fc/
How to reach support (FAQ) -
-steve
Microsoft MVP Windows Live / Windows Live OneCare, Live Mesh, & MS Security Essentials Forums Moderator