Knowing what versions you are working with would be helpful. However, another
alternative is to play it safe by using the oldest format available. If your
presentation does not use many advanced or newer features (such as animation,
sound, etc.) you may be able to save it in PowerPoint 95 format.
Start by doing a “Save As†and under the “Save as type†dropdown choose
“PowerPoint 96 (*.ppt)â€. This format should be compatible with older
versions. But remember, many advanced features and some fonts may not show
properly.
If you are using PowerPoint 2003 you may get around the font problem by
selecting “Toolsâ€, then “Options†and on the “Save†tab select “Embed True
Type Fonts†and click “Embed characters in use only (best for reducing file
size.)â€
By all means, you will want to try this out at least one day prior to your
presentation.
I hope this helps. Good luck!