PowerPoint 2007: Change Default File Save Format
Posted on Jul 18, 2008 under Office Tips |Are you tired of saving your PowerPoint 2007 files in a format that most people can’t read because they don’t have a version of the software that can view the file? Change the format that your PowerPoint 2007 presentations are saved in by default with these steps.
1. In PowerPoint, click the Office Button and select PowerPoint Options.
2. Click Save on the left.
3. For Save file in this format: select the format you wish to save your PowerPoint files in.
4. Click OK when you’re done.

by Mike Koutnik, on July 23 2008 @ 11:29 am
I have the opposite problem. I wan to change the default TO .pptx, and PPT 2007 wont accept the chance. I can select .pptx, but when I go back to Options, it is changed back to PPT 97-2003.