An alternative to placing the PowerPoint file on this site, would be to place it out on one of the free cloud file servers and just create a link to that site.
BTW, your other issue is due to the fact that a ".pps" (or the newer ".ppsx") file is a PowerPoint Show file -- not a PowerPoint Presentation. A Show file is automated. If you have PowerPoint, then you can convert it to a PowerPoint presentation file by opening it in PowerPoint, and then using "File->Save As" and changing the file format to ".ppt" (or ".pptx). See the following article ...
http://www.ehow.com/how_5548073_convert-pps-ppt.html
If you don't have PowerPoint, then you could convert it in OpenOffice or Google's Office. Although those will read PowerPoint files, they would probably save the file in a different format and extension than PowerPoint.