Can I add to my site advertisement not provided by AlterVista?
No. Every direct or indirect earning in money like discount tickets, points, virtual credits or other is not allowed by AlterVista's regulation.
The banners provided by AlterVista are the only ones allowed. You can find the HTML code to add them on your site in the "Revenues & Ads" section of your account's control panel.
Anyway simple banner changes and links to friend sites are allowed, as long as they do not generate any profit!