Hello,
The company I work for is about to begin testing for a transition from IE6 to IE8. One of our main concerns is about using permissions to control intranet access to internal sites,etc.
This was a problem we encountered during testing for IE7 and scrapped it all together. However, IE6 has more than its foot in the grave, its head is peeking out. Microsoft is only supporting IE6 until 2014 when they also abandon support for Windows XP. IE7 just came up with a box asking for you to enter your credentials. It didn't matter if you had permissions, it always said access denied.
We have yet to begin testing but I was hoping someone has encountered this issue as well and may be able to shed some light on the subject.