I think it's available in both Home and Professional version but, like any other module, in Pro version it is even more configurable... specially on virus cleanning (automatic actions).
Do this:
1. Control Panel > Video properties
2. Screen Saver tab
3. Choose avast screen saver
4. Click 'Configure'
5. Inside of its configurations, choose your 'own' screen saver and other details.
6. I could say more but I know it will be only in professional version...
