What's happening here is your presentation is showing in the
proportions of the document it's created in (e.g. 4:3), but your
computer has a wide-screen monitor. I think your resolution is either
1920x1200, 1680x1050, or 1280x800 (if you go to your desktop, right-
click and select "properties" then click on the "settings" tab, you
can find out which one you are). To make a presentation that displays
fullscreen, (in PowerPoint) go to File --> Page Setup..., and use a
width that corresponds to your screen proportions (e.g. 19.20 inches
by 12.00 inches for 1920x1200). That should fix it for you. Of
course, remember that if someone else plays the same presentation on
their computer that has different proportions, they will get black
boxes either on the sides or on top (for example, most projectors are
in a 4:3 ratio, such as 1024x768).
Hope that helps,
Kevin