That is not a boot scan that you are seeing, check your startup entries in msconfig, startup tab (windows start, Run, type msconfig and click OK, startup tab). The only avast entry should be, ashDisp.exe, for the avast icon in the system tray.
There is no preference for enabling what you are seeing, so equally there is no preference/setting to disable it. To see what you are seeing you have to have manually set it up. Has anyone been tweaking either msconfig or the startup folder ?
Well you shouldn’t need ashWebSv.exe as a start-up item either as you are using XP and the only startup should be ashDisp.exe. How did these extra startup entries occur ?
With XP and avast, if you have the Web Shield provider enabled then there should be an XP Services entry for it, set to Manual so after boot the web shield provider should be started it doesn’t require a conventional startup entry.