Opening PPS files received as Outlook Express Attachments

When I try to open .pps files when received as attachments in Outlook Express e-mails I receive an error message that I need to associate the file with a program to open it in Folder options in control panel. I have done this but the error message still occurs. If I copy the file onto my desk top I can open it with no problem ( it opens with Power point viewer 2003 that is installed with MS Works Suite) Other attachments e.g WMV files seem to open from outlook express with no problem.

I wouls be very pleased to receive any advice that might help.

Thanks