IE4 can do this with multipart/related.  Just do File/Open on the MIME...

-----Original Message-----
From: Jacob Palme <[log in to unmask]>
>Note: In the future, web browsers will probably be able to take a whole
>document of Content-Type: message or Content-Type: multipart as one single
>file to be displayed. When web browsers get this functionality, the
>problems described below will be much easier to handle, just send the whole
>combined MIME message as a single file to the web browser.