Apparently IE handles floats differently and having a 7em margin on both div#nav and div#main is causing the problem here. Don't have a solution for you.
Yeah, I would not believe them either. What you are using is actually called a "script behavior", and there is a separate setting for enabling or disabling such things, which falls under "ActiveX controls and plug-ins" as "Binary and script behaviors". So there are at least two settings that have to be enabled, that one and the one for "Active scripting".
Perl / MySQL / HTML+CSS