You might also have luck by trying to fake things out with PATH_INFO. We're straying off-topic here, but here goes: start with the URL you have right now:

http://www.example.com/foo/powerpoint.html
[download]

Tack on the end more stuff. The browser won't know which part of the path is the file name and which part is the PATH_INFO, although the server figures it out when it does its path walk.

http://www.example.com/foo/powerpoint.html/no_really_i_mean _it.ppt
[download]

If the browser gets to the point where it's going to decide the type based on the URL (or choose a file name to save it as), then this sometimes works. That trick is especially handy when a script returns the content, but you don't want the script name as the file name.

http://www.example.com/cgi-bin/make_ppt.cgi/no_really_i_mean _it.ppt
[download]

The trick is to use a lot of techniques all at the same time.

Another piece of advice you didn't ask for: even though you are targetting IE, you might consider developing with a browser like Firefox. When you do that, you have a better chance of figuring out if its the server or the browser that's wrong. You still develop with IE, but the other browser is a check: if the server is wrong, it should (should!) be wrong in both browsers.

I really don't miss my days as a web developer, when we had to support WebTV too. :)

Good luck :)