Well, the other night I did some research to figure out why Microsoft's latest and greatest MacOS browser, 4.01, still doesn't know how to download a file in this manner. What I found is really quite surprising. I used Peter Lewis' fabulous CGI debugging tool, OTSessionWatcher. It captures TCP data streams to show what's going on behind the scenes. That is, it shows you the data before your browser mangles it.
Navigator puts up a file dialog and asks where to save the file.
Using the same form with MSIE, a very weird thing happens. Now for the response. This is where it gets weird. There's the file. Pity IE ignores it and for totally unknown reasons issues a second, duplicate request.