I just brought my third one of these:
(my first got lost at an event a few years ago, and I lost the USB dongle for my 2nd a few months ago)
If you want something to change your PowerPoint (or powerpoint-like) slides, this is the tool to get. Its worked with every computer I've tried it on, and every piece of presentation software (PDF viewers and HTML slidy in addition to PowerPoint and Open Office).
No software to install either - the dongle appears as a USB keyboard - the four keys send PgUp and PgDown to change slides; the laser beam button sends an F5 (which is start-presentation in PowerPoint) and the bottom button sends 'b' (which is blank screen in PowerPoint).