I forwarded the two messages to my work account (where I use Lotus Notes 4.6a to read mail), munging the headers a bit as I did so in order to make sure I could actually see the MIME as Lars sent it.  Here's what I got.

MIME Test One:

Each of the thick black bars is left-clickable, and brings up a pop-up dialog showing the type of that part: "text/plain" for the first (horizontal) bar, "image/jpeg<newline>Local Attachment Info --> JPEG File Interchange" for the second (vertical) bar, and "text/plain" for the third (horizontal) bar.

When you double-click (or single-right-click) on att1.jpg, you have the option of "Launch"ing an external application for it, or "View"ing it within a Notes window:

MIME Test Two:

Each of the thick black bars is left-clickable, and brings up a pop-up dialog showing the type of that part: "text/plain" for the first (horizontal) bar, "text/enriched" for the second (horizontal) bar, "image/jpeg<newline>Local Attachment Info --> JPEG File Interchange" for the third (vertical) bar.

The att1.jpg icon behaves just as in MIME Test One.