Mark Russinovich and Scott Hanselman recently presented on the SysInternals Suite at the Ignite conference. The SysInternals Suite contains a number of great low-level Windows tools, but most interestingly it contains an awesome, free, and lightweight presentation tool called ZoomIt.
ZoomIt written in C, so it easy to download and run without any complex installation process. After downloading and unzipping, run ZoomIt.exe (or ZoomIt64.exe on 64-bit Windows) and it will start running and place an icon in the system tray (lower right corner of the desktop). You can right-click on the tray icon and select Options to open the ZoomIt configuration window.
With ZoomIt running, press Ctrl + 1. You will notice the screen zoom in slightly. You can then use the mouse wheel to zoom in or out as needed. You can also move the mouse to pan around the zoomed screen image. You can press the Escape key or Ctrl + 1 again to exit the zoom functionality.
This is the best feature. While you are zoomed in, you can click the mouse anywhere to start drawing a line. Holding the shift key while drawing will draw a straight line. Holding the Ctrl key while drawing will draw a box. Holding Ctrl + Shift while drawing will draw an arrow.
You can press "e" to erase all the lines.
If you want to draw annotations without zooming, start instead with Ctrl + 2.
Press Escape to reset everything (stop zoom and erase any lines).
You should consider using ZoomIt to enhance your presentations and add emphasis to your main points.