Outlook shows no pictures

I`m puzzled.
In a 45 user environment, 2 users have an issue with outlook.

When a mail gets sent with an embedded image – the image does not show – just a blank space.
However, when these users do a Reply or Forward, then they can actually see the images.
Other users have the same settings, same version of Outlook (2003 with all patches to date installed).

Is there something, probably user specific, that could cause this – and if there is, how can i solve this?
It`s annoying, and we have a workaround, but the users would like to see the pictures at once.

Oh, it doesn`t make a difference if they view in in the preview pane, or as an opened message.