Any update after October ~10 makes my computer unusable

[gchiozzi]

Dear all,

I have an XP PC and I am using Avast Home since years, together with Zone Alarm as firewall.
The PC had automatic updates of Avast active.

Starting from around October 10, any update of Avast makes my computer unusable:
   - It does not complete the login if there is no internet connection
   - Even in tat case, the Windows Desktop (taskbar, explorer....) almost immediately
     hang.

CPU usage is very slow, but even the task manager becomes unresponsive.

I have seen that reinstalling a hard image of my system I took on the 15th of September works
fine until I try an update of Avast database and program.

The update seems to work fine, but at the next reboot everything gets sloppy and unusable as described above.
Any idea?
I did not manage to find anything similar but for this post:

         http://forum.avast.com/index.php?topic=50300.0

But nothing has change in my computer with the exception of Avast update.
I could really verify it using the TrueImage backup of my complete system.

Another PC I have  (also with Zome Alarm) works fine.

I will be grateful of any help!!!!
Otherwise I will have to uninstall the Avast and try to switch to some other program.

      Thanks in advance.

[gchiozzi]

Looking again I found another post that might be related:
     http://forum.avast.com/index.php?topic=48814.15

I do not have the same effect, but dates looks similar.

Something bad happened with the Avast updates starting from the beginning of October.

Can anybody relate these posts and come with an idea?

      Cheers.