Verified answer

Right-click your desktop and select either Properties or Personalize and look at the display / screen resolution settings. It sounds like you have a 4:3 image being centered on your widescreen monitor.

Monitor Black Border

I don't know how Vista works but you could try right clicking the desktop to get to the display settings, click on advanced, and change the monitor setting's screen refresh rate.

Fiddle about with the monitor positioning or update your graphics driver

If it's not that then give your nephew a good slap

hold down the ctrl key while scrolling your mouse