I was fortunate enough to attend Microsoft’s Tech-Ed event in Berlin in Nov 2009 and whilst at the conference, most of the presenters used a useful utility to zoom in on different areas of the screen, to highlight things to the session attendees.
I found out they were using a free piece of software called Zoomit.
ZoomIt is a 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. ZoomIt works on all versions of Windows and you can use pen input for ZoomIt drawing on tablet PCs.
I will definately be using it for my future computer presentations. Download it from here
Elon's Blog 