Cyclokay,
I think you mean 0020-80070643.
If so, you can refer to this knowledge base article to troubleshoot 0020-80070643 installation error message.
http://support.microsoft.com/default.aspx/kb/930162Also try removing all other security applications you have on your computer, before installing onecare.
If none of this helps. Please contact support.
How to reach support (FAQ) -
http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90