In CMS we have a software feature that allows users to export any screen in the application as an MS Office file (Word, Excel or PowerPoint). Recently we found out this feature didn't work very well for some Internet Explorer 6 users, so we had to tweak our implementation a bit.
The basic technique we use to create MS Office files is to take our existing HTML screens and instruct the user's PC to open the files in MS Office. In the past, we told the PC to open the file in MS Office by setting the MIME type for the appropriate file type (e.g. application/ms-word for Microsoft Word). We found a technique that works better with IE6, HTTPS and MS Office is to set the Content-Type to application/x-download and set the Content-Disposition to attachment; filename=(filename here).
We learned of this technique by reading this article from ONJava. The article is written assuming a Java programming environment, but setting HTTP headers isn't really specific to Java, so the basic technique should be applicable to any web environment. If you've been wrestling with IE6, HTTPS and MS Office, I hope this article is of some help to you.