The question is: How do I open/view/edit a PPS file in PowerPoint?
The Simple Answer: PPS files – technically speaking – ARE PowerPoint files. The only difference here is that PPS opens automatically in a different mode and shows you in presentation mode and in full screen. There’s a quick solution to this: In Windows Explorer, just edit the filename from something.pps (or something.ppsx if you have a newer version of Microsoft PowerPoint) to something.ppt (or something.pptx, respectively). That should do it – now you are able to edit it as you wish with PowerPoint.
If the problem is that you don’t have PowerPoint, you need to download the PowerPoint Viewer 2007, in order to view them (you cannot edit them with the Viewer though).