For Windows Integrated Authentication to work automatically, without prompting the user everytime, "Internet Explorer must consider the requested URL to be on the intranet(local). If the computer name portion of the requested URL contains periods (such as http://www.microsoft.com and http://10.0.0.1), Internet Explorer assumes that the requested address exists on the Internet and does not pass any credentials automatically. [...]
Still waiting to see what Microsoft has to say, they are running late. Live from Microsofts mystery press conference in Los Angeles! -- Engadget.