I picked this information up from a Dave Hayden blog post.

ZoomIt is a Screen Zoom and Annotation Tool for Technical Presentations created by Mark Russinovich and it is FREE!

Here is a brief description of the tool from the download page:

ZoomIt is screen zoom and annotation tool for technical presentations that include application demonstrations. ZoomIt runs unobtrusively in the tray and activates with customizable hotkeys to zoom in on an area of the screen, move around while zoomed, and draw on the zoomed image.

I downloaded the application and tried it out in my Visual Studio 2008 IDE.  It worked great and it is super easy to use.