OK, thanks.
Did you know that there are actually 4 sharepoints - all very different products?

Anyway, I confirmed that avast! should work with Windows SharePoint Services 2.0. You should use the "SharePoint 2003" to provide the protection. Did you install this provider?
Also, what happens if you try to access the SharePoint AV interface?
Click Start, point to Programs, point to Administrative Tools, and then click SharePoint Central Administration.
On the SharePoint Central Administration page, under Security Configuration, click Configure antivirus settings.
Thanks
Vlk