Hmm... I'm running out of ideas.
Maybe DrWatson could detect something... please, start
drwtsn32 -i
(it will set up DrWatson as the default debugger).
When the avast! window disappears during the scan, it's possible that DrWatson collects some information about the crash. Check the corresponding folder; by default, it's
C:\Documents and Settings\All Users\Application Data\Microsoft\Dr Watson
Are there any recent files there?
Thanks.