May help:
If pics are CMYK rather than RGB they won't show in the body of Outlook Express email. This is burried somewhere in the small print, but not widely known. You just get the boxes with red x. Attachments will be fine, but they won't show in the email body.
Also, when MAC users send pics in emails to PCs, there are sometimes small pic files that accompany, but do not open (and are not required). Usually with same name but smaller...