Begin your slideshow by pressing the F5 key, or by selecting From Beginning or From Current Slide in the Start Slide Show group on the Slide Show tab.
During the slideshow, hold down the Ctrl key and the left mouse pointer to make the laser pointer appear on the screen.
Drag your mouse to move the pointer across the screen.
You can change the Laser pointer color by selecting Set Up Slide Show in the Set Up group of the Slide Show tab.
You can select from red, green, or blue from the Laser pointer color dropdown, then click OK.
View the original article: http://www.howtogeek.com/howto/19924/use-your-mouse-as-a-laser-pointer-in-powerpoint-2010/
24th June 2010