I have received a number of e-mails that I cannot open because my system does not acknowledge it. All the e-mails have a joke that was sent to me. The problem is that they all end with a .pps which I cannot open. Can you advise. Thanks for your time.

You need to have Microsoft PowerPoint installed to view them.
You can try installing the free PP viewer from here:
http://www.microsoft.com/downloads/details.aspx?FamilyID=428d5727-43ab-4f24-90b7-a94784af71a4&displaylang=en