I am using a Mac, system 9.2.2.  My email is Outlook Express, version
5.02.  Often when I click on "reply" there is a blank space where one
or more of the previous emails have been.  I would like the entire
chain of emails to always appear when I reply.  What's happening, and
how do I correct it?

What is happening is someone is sending you an e-mail that OE is not
recognizing the content of.  The same thing happens in older versions
of Eudora with HTML content.  The workaround in that case was to
Ctrl+C to copy and then Ctrl+' to create "quoted" content.  If you can
read it, it might be possible to copy the text in advance of replying
and then paste it into the reply, but I am not aware of a hotkey that
will cause the pasted content to be "quoted".  You might be able to
get away with not quoting by color-coding the text you paste.

You could also try another e-mail client like Thunderbird or, um, Pine.