The most noticeable area of change is at the top of the PowerPoint window. Instead of the menus and toolbars that you used to see, there's a tall band across the screen that contains many, very visual commands arranged into groups.
This band is called the Ribbon, and it's now your control center for creating a presentation. You'll get some background on its design and see its structure in detail so that you start to feel comfortable using it.
Find out about other aspects of PowerPoint 2007, like keyboard shortcuts, the Quick Access Toolbar, and more.