Tutorial
How to set the default program to always open the slideshows with the PowerPoint Viewer
1) Right click on the slideshow file on your computer, select 'Open With', and click on 'Choose Program'... Then click on the 'Browse' button.
2) In Windows Explorer, navigate to 'Program Files' and open the folder 'Microsoft Office'.
3) Find and open the folder 'Office 12'. Select 'PPTVIEW.EXE' and then click on 'Open'.
4) Check the box 'Always use the selected program to open this kind of file. Click on 'OK' and your done.

