This has been possible up to .Net4.0 and IIS 7.5.
The general idea is that you enable anonymous and forms authentication for your intranet site and in a subdirectory you enable windows authentication together with forms authentication and turn off anonymous. By disabling the forms 401 => 302 redirection with some custom code you will be able to get a hold of the users username and domain.
If you google for a solution all roads seem to lead to this blog/solution: http://mvolo.com/iis-70-twolevel-authentication-with-forms-authentication-and-windows-authentication/
However when upgrading to .net 4.5 and IIS8 it breaks, Always forcing a 302 redirect to the login page and no means of getting a hold of the usernamen.
Has anyone solved this yet?