If you are using Windows XP or higher, ZIP is built in. If there are no
external files, you can right-click on the file (or the folder it is in if
there are other files that you need that are in the same folder) and choose
Send To > Compressed File.

You might also try the free PFC Express, which is made for this purpose.
You can find that at http://www.playsforcertain.com/

--David

You can use a Powerpoint to video or PowerPont to Flash tool to reduce
the file size.
Convert PowerPoint to mp4 video can reduce 60% of your ppt file:
http://www.ppt-to-dvd.com/ppt-to-video-overview.html
Convert ppt to flash can reduce 80% of your ppt file: http://www.sameshow.com
All the videos, audios, transitions animations can be retained

Phil/Molly

These days zipping (compressing) a powerpoint file will only shrink the file
a little bit.

see
Why are my PowerPoint files so big? What can I do about it?
http://www.pptfaq.com/FAQ00062.htm

Or see something like
http://www.nxpowerlite.com/index.php?ld=n

Cheers
TAJ Simmons
microsoft powerpoint mvp

awesome - powerpoint backgrounds,
http://www.awesomebackgrounds.com
free powerpoint templates, tutorials, hints, tips and more...

You can convert your powerpoint presentation to video or flash.
For this task take a look at Presentation To Video Converter
http://www.geovid.com/Presentation_to_Video_Converter/