Areas are ment to be used for more static page structures such as organizational units (HR, IT, production etc) where sites are ment as presenting more ad-hoc kind of data such as project rooms, discussion fora etc.
Sites comes with WSS (Windows SharePoint Services), areas comes with the SharePoint Portal Server (witch also has sites just to confuse things even more ;-) )
For sharepoint stuff i use either usenet (microsoft.public.sharepoint.portalserver(.development) or microsoft.public.windowsservices(.development)) or MSD2D.com
//AndersR