It is good to see lot of people with same problem as mine here in Italy !
My laptop:
- Sony VAIO VGN-BX61XN
- Windows Vista Business with SP1
- Intel PRO\WIRELESS 3945/ABG
-
Other software
- Spybot
- Avast
- Zonealarm

I am fighting with this problem since 1,5 month !

I tried everything you listed here except: to disable AVAST webshield, to disable Zonealarm,and to deinstall spybot. I will do it asap.

Who is familiar with NetMonitor can tell us what happened on the network during the issue.