Error 643
Install the Updates manually
the easiest way to download any update Microsoft releases and do this
manually is to plug the KB######'s into this web page:
http://support.microsoft.com/kb/######
In this case:
http://support.microsoft.com/kb/974234
From which you should click on the link for IT Professionals:
http://www.microsoft.com/technet/security/bulletin/ms09-060.mspx
Where you can get the proper update for your version of Office.
They will also want to check the original link given to ensure they meet the
"Prerequisites to install this security update" and they might even utilize
the section on "How to obtain help and support for this security update" to
their advantage.
Error 646
Possibility: Windows Update agent file Wups2.dll is registered incorrectly
and registry files that relate to the Wups2.dll file are missing.
Method 1: Register the Windows Update files
1. Click Start and then type notepad in the Start Search box.
2. Click Notepad in the Programs list.
3. Copy the following commands, and then paste them into the opened Notepad
window:
REGSVR32 WUPS2.DLL /S
REGSVR32 WUPS.DLL /S
REGSVR32 WUAUENG.DLL /S
REGSVR32 WUAPI.DLL /S
REGSVR32 WUCLTUX.DLL /S
REGSVR32 WUWEBV.DLL /S
REGSVR32 JSCRIPT.DLL /S
REGSVR32 MSXML3.DLL /S
4. In Notepad, on the File menu, click Save As.
5. In the Save as type list, click All Files.
6. In the File name box, type register.bat.
7. Save the Register.bat file to your desktop.
8. Right-click the Register.bat file, and then click Run as administrator.
If you are prompted for an administrator password or for a confirmation,
type the password or click Continue.
9. Try to install updates again.
http://support.microsoft.com/kb/958053
see: Method 1: Register the Windows Update files
http://support.microsoft.com/kb/326253
Method 5: Register Windows Update engine files
http://support.microsoft.com/kb/971058
How do I reset Windows Update components?
Method 2: Download and install the Windows Update agent
Windows Update Agent
How to obtain the latest version of the Windows Update Agent to help manage
updates on a computer
http://support.microsoft.com/kb/949104
Information for network administrators about how to obtain the latest
Windows Update Agent
http://support.microsoft.com/kb/946928
Click Start, click Run, click Browse, locate the file that you saved and
then click Open.
Add the /wuforce switch to the end of the run command, and then click OK.
For example, the run command may appear as the following:
"C:\WindowsUpdateAgent30-x86.exe" /wuforce
Click Run.
Follow the steps to complete the wizard.
Important
To reinstall Windows Update Agent - download the relevant file from one of
the links provided above and save it to a drive where Vista is not loaded
because the file cannot be launched directly from the system root directory.
Click Start, click Run, type: "D:\WindowsUpdateAgent30-x86.exe /wuforce"
(without quotations) and then press Enter to install the Windows Update
engine.
Note: There is a space between "D:\WindowsUpdateAgent30-x86.exe" and
"/wuforce"
D: is the drive where Windows is not installed (ie a flash drive or a 2nd
hard drive etc)
Finally
See the "How to obtain help" section of
http://support.microsoft.com/kb/960859