New problem found for you guys [:)]
When Logging into an exchange web through transparent proxy I get a page timeout in IE6/7 but it works fine in Firefox 3.0.5
The password prompt does come up but once logged in the page times out in IE, the site does work however if I specify a proxy within the browser to point to the firewall instead of using transparent mode.
---Edit---
Ooops forgot to mention it's Exchange 2003