Since PowerPoint 2007, Microsoft removed the feature that let you compare your presentation with another one — that was great if you had send your presentation to a colleague and he or she made changes you were not aware of. You can however place both presentations side by side and compare individual slides — not too great a workaround, but it does allow you to compare the slides.
Learn how you can view presentation slides, side by side in PowerPoint 2010 for Windows.

