To uninstall Windows Live OneCare from Vista:
Note that part of the uninstall will ask you to provide a reason for removing OneCare.
If Windows Live OneCare does not uninstall as expected, download the Windows Live OneCare cleanup utility - http://social.microsoft.com/forums/en-US/onecareinstallandactivate/thread/399071e2-49dc-4767-932d-d261e3965943/ and follow the program instructions to completely uninstall.NoteYou will be prompted to restart your computer. You must restart your computer in order to completely uninstall Windows Live OneCare.
If you are still unable to remove Windows Live OneCare, you can contact support for help -
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90