Open PowerPoint and then do the following:
1. Go to View > Master > Slide Master.
2. Go to File > Save As and click on "Design Template .POT" in the "Save as file type" box.
3. The "Save In" box will show the folder where PPT plans to save the file. Click the arrow on the right hand side of this box and the drop down menu will show you the full path to the folder where your templates are expected to be.
4. Exit PowerPoint and place new templates in the correct folder, or create a new folder at the same level and save them there. I like that method because I can have a folder called "\My Templates", for example.
5. Open PowerPoint and go to Format > Slide Design and you will see all of the available templates in the Task Pane.
If you are using PowerPoint 2003, please see the tutorial at http://www.soniacoleman.com/Tutorials/PowerPoint/powerpoint_2003__templates.htm
For PowerPoint 97-2002, please see the tutorial at http://www.soniacoleman.com/Tutorials/PowerPoint/powerpoint_templates.htm