Opening attachments in Outlook Express
 

When I receive a .pps attachment via email, and click to open, an alert window pops up saying "This file does not have a program associated with it for performing this action. Create an association in the folder options control panel"
The association is already there,(and has been since I downloaded powerpoint) and works fine if I save the attachment to the desktop (or a non- outlook express folder) and open it from there.
Windows XP,SP2, 2 hard drives, OS on one, all downloaded (non-XP)programs/personal files on the other. Outlook Express 6. I'm part-dummy/part not too ignorant. But ignorant about this one.
Any help please?