There is this Presenter View that provides you with this functionality.
Access it through "Slide Show" | "Set Up Show..." menu item, check "Show
Presenter View" box, click OK. In a multi-monitor, when you start the slide
show, the Presenter View shows you the notes while the projector shows the
slide show.
- Chirag
PowerShow - View multiple PowerPoint slide shows simultaneously
http://officeone.mvps.org/powershow/powershow.html