View > Master > Slide master. I am trying to remember how this was in version 2003, it has changed. The thing you want to be careful in 2003, is that if you aren't careful, you will change every single slide, not just most of them.

I would go to Slide master view and then insert a new master and add the placeholder, and whatever else I wanted for every one of these slides. When you leave Slide master view, the new design appears in the Slide Design task pane under Used in this presentation.