Hi,
On Windows XP Avast cannot be updated behind SBS 2003 Premium with ISA.
I configure ISA to let pass all http request to *.avast.com.
On the Windows XP we can type http://www.avast.com and it works. And this problem is not only on one SBS I can reproduce this trouble on 3 differents SBS network. 
If I uninstall ISA the trouble stay the same.
Any idea ?
Regards.
GG.
Updates are running under local system account, you’ll have to allow internet connection for this account in ISA.
If it doesn’t help, send me file setup.log from avast4\setup folder.
You can get on http://sbsfr.free.fr/setup.zip
In the zipped file you have setup.log
thank’s for help.
PS : I have two other sbs (especially my SBS) in the same conf and I don’t reproduce this kind of troubles.
Regards.
GG