I had the same problem in Windows Vista. I was using powerpoint viewer but it would not work from my email. Downloaded a PPS file to the hard drive where you can find it. Go to the file and right click on it. Select "Open With". If "Powerpoint viewer" is there select it. If it is not there click "choose default Program". Go to computer,local disk c:, program files, Microsoft Office, Office 12, then Select "PPtview.exe. Now your pps files should work from your email.