Hello John,
I'm not sure whether you have attempted to recover your system or not because of issues with Windows Update. You might be able to try a system restore and see if you can get back to before you were having problems with Windows Update.
The error code 80070643 is a generic error that basically state that an error was encountered by Windows Installer.
Mark was correct in stating that you seem to have more problems than just with Windows Update.
However, you might want to look at the following KB article to see if this will help with the Error 80070643.
KB958052 - You receive error code 0x80070643 or error code 0x643 when you use the Windows Update or Microsoft Update web sites to install updates
http://support.microsoft.com/default.aspx/kb/958052
Please post again and let us know your status and if we can help in any way with getting your system back to a working state.
Sincerely,
Marilyn
Microsoft Answers Support Engineer
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