First, ensure that these Services are set to these Startup types:
Background Intelligent Transfer Service (BITS) - Manual
Windows Event Log - Automatic
Windows Installer - Manual
Windows Modules Installer - Manual
Windows Update - Automatic (Delayed Start)
If they are or were, suggest you clean boot Vista:
How to troubleshoot a problem by performing a clean boot in Windows
Vista or in Windows 7
Once Vista is in the Clean boot state, ensure that the native Windows
firewall is Enabled as the system must be connected to the internet when
you do the next steps:
How do I reset Windows Update components?
Click the Fixit button and choose to *save* MicrosoftFixit50202.msi.
When the download completes close all open programs and browsers.
Now run MicrosoftFixit50202.msi and choose the *Aggressive mode*.
When the Fixit has finished it is operation, restart the system.
While *still* in the Clean boot state, see if the system can search for,
download, and install updates now.
If it can, then AVG9 was the most likely culprit of the updating issue.
UNdo the Clean boot steps, restart, and see if the system can check for