when using Microsoft Outlook, and preparing an email, when I used to
add an attachment, a horizontal line would appear in the body of the
email and all attachments would appear below.  This has now
disappeared and I would like to know how to get it back.

This 'problem' only happens when you are sending an email in
'Microsoft Outlook rich text format'.

Change your mail format to HTML or Plain Text and add an attachment
and the horizontal line will be used.

You can change the mail format in Tools->Options->Mail Format

orezzero is correct. I had this same problem with Outlook 2002 (XP).
After researching the problem, I found that the attachment "bar" will
not appear if you are sending messages in Rich Text format. Switching
to Plain Text or HTML fixed the problem.