The Compatibility Checker dialog box lists which things will be affected if you save to an older format. You can click the Help link to get more details.
What about all the presentations you have that were created in earlier versions of PowerPoint?
There's no problem opening and editing an older presentation in PowerPoint 2007. What you'll need to decide is whether to keep the presentation in its original format or save it in the new format.
PowerPoint 2007 helps you make the decision; here's how.
Checking for compatibility
PowerPoint 2007 recognizes the presentation, when you open it, as being in the old format. So behind the scenes, it takes note of anything you add to the file, such as a shiny new SmartArt graphic, that may not work exactly the same in the old format.
Then, when you click Save, PowerPoint displays the Compatibility Checker dialog box. The checker details what will happen to PowerPoint 2007 elements if you save the file in its original format, PowerPoint 97-2003 Presentation (.ppt). (The picture illustrates this.)
You can cancel the checker and select the new format in the Save As dialog box. Or, you can choose to continue and save in the old format. We'll look more at that choice in the next section.