[Zope] IE Auth failures, NS works fine

Please excuse my ignorance in this matter. I know nothing about Windows. I have posted this before but have had no luck with a solution. I thought one more try here and then I guess I migrate to Enhydra or something. Anyway, I have a site with about 300+ users running on Redhat 6.1 with Apache serving Zope. Auth is handled by GUF, but I don't think GUF is an issue. I've been fielding problems authenticating with Internet Explorer for about a month now. The solution? Use Netscape. It works perfectly. I don't think this is very acceptable, however. Can't anyone help me track this down? I have no idea where to start looking in Windows to figure this out. I have no idea what questions to ask. Why is a browser not a browser? TIA jim