Solution for Windows Update Error Code: 0x80070643

This may have been posted already - if so - my apologies - This worked for me.
Along with not being able to run this update - I could not run a detect and
repair on my outlook. So I found this
http://support.microsoft.com/default...;EN-US;Q315346 KB aritcle.
The steps listed here resolved my detect and repair issue.
Right after running the detect and repair, I ran the Update for Outlook 2003
Junk Email Filter (KB911961) and Security Update for Outlook 2003 (KB892843)
successfully. It's been haunting me for about 2 mos now.

Good luck