How do I insert a slide from another powerpoint presentation?
There is a better way. In 2007 and 2010 go to the "New Slide" button drop-down. At the bottom, choose "Reuse Slides". It will open a pane where you can browse for the other PPT file. It also gives you a checkbox to "Keep Source Formatting" if you desire.
In 2003, the same feature was under the "Insert" menu and then choose "Slides from Files"