Downloading Office files without opening them

I have a website which provides my users with alot of downloadable files, most of which are Microsoft Office documents (ppt's and doc's mainly). These are generally quite large files due to the nature of their content.
Because of their file types, on most users machines (those that have the relevant office plugins for IE) Internet Explorer displays the files within a browser window, rather than showing the user the download dialog box with the 'Save or Open' options.
The problem is that because no dialog box is shown the user gets no visual indication that anything is actually happening, and as my files take a long time to download my users often think that nothing is happening and close the browser window.
What I would ideally like would be for IE to treat the office files like any other file - i.e. show the 'Save or Open' option and then show a progress bar while the file downloads. Does anyone know a way to achieve this?
Maybe by tricking IE into thinking it can't open the files somehow?
Or maybe by some other method?

Thanks, James.

No answer springs directly to mind but how about not using such large files, if you use a .pdf instead then it should load a lot quicker.

Oh no wait, I do know the answer, .zip the files and that'll force the dialouge box.