PowerPoint does a lot of its own compression. That is probably why the
file size is not reduced much by zipping. There is no difference in the
file as a PPS or PPT. The files are the same. The different extension
tells PowerPoint to open it as a show. You might want to check out this
information about reducing file sizes in PowerPoint:
--
David M. Marcovitz
Microsoft PowerPoint MVP
Director of Graduate Programs in Educational Technology
Loyola College in Maryland
Author of _Powerful PowerPoint for Educators_ http://www.PowerfulPowerPoint.com/