I just got XP about six months ago. I think PPS was not one of the file
types listed under Folder Options, but PPT was. So I added a PPS type and
told it to open with the Power Point viewer.

When I get an e-mail with a .pps attachment, it won't open when I
double-click on the attachment line. I get the "Unknown file type", "No
program associated with this type of file, etc." However, if I save the
attachment, it will open from Windows Explorer.

So why won't it open by double-clicking on the e-mail attachment line?