IE8 and internal sites connectivity problems

My hand’s been shoved into pushing out IE8 to our users. During testing, I’ve discovered that IE8 won’t display some (not all) of our network server web apps, unless I click “Diagnose Connection Problems”, and then it magically works. My best guess has to do with either permissions in IE to access the site, or the DNS server it’s trying to hit is not our network DNS server.

Having users click “Diagnose Connection Problems” is NOT an option, and M$’s site for help on this is pretty much useless. The app works find in IE6, we’re skipping 7 to go right to 8.

Ideas are welcome, and shooting down IE8 won’t help (decision’s out of my hands). Going to another browser is also not an option.

*sigh*

Help!