Yes. PowerPoint 2003 shares the same file format as earlier versions back to
97, so earlier versions automatically be able to read the file. However,
some of the newer features won't work. You can disable the new features by
going to the Tools menu, selecting options, clicking on the Edit tab, and
check the 3 boxes at the bottom (under "Disable new features"). That will
prevent you from accidentally using any features that won't work in earlier
versions. If you want to go back to versions before 97, this is possible
too, but so much has changed since 95 that it might not be a good idea.
Finally, if you need to use the newer versions, your users can download the
2003 viewer for free. See:
http://www.rdpslides.com/pptfaq/FAQ00153.htm
--David
David M. Marcovitz
Author of _Powerful PowerPoint for Educators_
http://www.loyola.edu/education/PowerfulPowerPoint/