I recently was sent a presentation by a friend. It's one of a series of training files prepared in PowerPoint 2003. The files will open in PowerPoint 2003 and in Open Office but not in PowerPoint 2007. Attempts by PowerPoint 2007 result in long hang times and several error messages such as "Pres Esc to cancel". Up to now I've had no problem opening other ppt files with PowerPoint 2007. I won't upload one of the files here since they're ~14 MB and are proprietary.