Finally, we got official and detailed articles from Microsoft about Forms Authentication in SharePoint Server 2007 and Windows SharePoint Services 3.0:

• Forms Authentication in SharePoint Server 2007 and Windows SharePoint Services 3.0 (Part 1 of 3): Introduction: http://msdn2.microsoft.com/en-us/library/bb975136.aspx
• Forms Authentication in SharePoint Server 2007 and Windows SharePoint Services 3.0 (Part 2 of 3): Forms Authentication Samples: http://msdn2.microsoft.com/en-us/library/bb975135.aspx
• Forms Authentication in SharePoint Server 2007 and Windows SharePoint Services 3.0 (Part 3 of 3): Differences Between Forms Authentication and Windows Authentication: http://msdn2.microsoft.com/en-us/library/bb977430.aspx