Do you get literally just the text, or do you get "placeholders" (empty boxes with an X in the corner or similar) where the graphical bits should be?
If so, your problem might be an option on mail delivery - I don't have Outlook Express to hand, but most email clients have an option somewhere (probably well hidden) along the lines of "only retrieve graphics for senders in my address book".
What I suspect (but could be totally wrong) is that this particular colleague is not in your address book, all the others are, and the option is set.