The versions of PowerPoint (or PowerPoint presentations) still floating around are:
|PowerPoint 4||Office 4||Win 3.x, Win95, Mac|
|PowerPoint 95 (PowerPoint 7)||Office 95||Win95 or higher; no comparable Mac version|
|PowerPoint 97 (PowerPoint 8)||Office 97||Win95 or higher; comparable to PowerPoint 98/Mac|
|PowerPoint 98||Office 98/Mac||Mac; comparable to PowerPoint 97/Windows|
|PowerPoint 2000 (PowerPoint 9)||Office 2000||Win95 or higher; no comparable Mac version|
|PowerPoint 2001||Office 2001/Mac||Macintosh; halfway in between 2000 and 2002 Windows versions. Maybe that's why they called it 2001?|
|PowerPoint 2002 (PowerPoint 10)||Office XP||Win98 and higher; comparable to PowerPoint 2001/Mac|
|PowerPoint 2003 (PowerPoint 11)||Office 2003||Win2k, XP, Vista; generally comparable to PowerPoint 2004/Mac|
|PowerPoint X||Office X||Macintosh OS X|
|PowerPoint 2004||Office 2004||Macintosh OS X|
|PowerPoint 2007 (PowerPoint 12)||Office 2007||XP, Vista; generally comparable to PowerPoint 2008/Mac|
|PowerPoint 2008||Office 2008||Macintosh OS X|
Some versions of Office (Small Business Edition for example) do not include PowerPoint. See Which version of Office 2000 is right for me? for more info.
Generally, every version of PowerPoint can read and save files in the format of several previous versions of PowerPoint. Since older versions don't support some of the features of newer versions, backward compatibility isn't complete.
Moving a presentation back and forth repeatedly between versions, especially between PowerPoint 2007/2008 and earlier versions, or between PC and Mac versions of PowerPoint will make your hair fall out. Small children will run away from you. Dogs will growl at you. And the world will generally not be your oyster. So don't.