If you are trying to install using a retail CD, don't use the CD but download the One Care trial from here -
http://onecare.live.com/standard/en-us/default.htm To activate the trial after installation open One Care and select the "Subscribe" buton. Follow the prompts and when you get to the payment page select "Pre-paid PIN or Token" as the payment method, then enter the 25 character product key. If this does not resolve your installation issue please post back the installation problem you are having in as much detail as possible or contact support. How to reach support -
http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2