I tried to install Onecare, an error ID 0023-80070643 came up. I went through the steps of the resolutions still they don't help.
See this thread - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=3639719&SiteID=2 - for Jim's reply.
There is a missing update on your system that is failing to install and it is required to be installed before OneCare can proceed with installation.
-steve