I suppose you have photos? FIrst of all, you should compress the pictures
before inserting them in PPT. FOr video a wmv generally is lighter than an
avi. A riff wave has the weight of an MP3 that is lighter than a wave.
With PPT 2003 and before, I use NXPowerlite to compress the presentation
with very good results.
In addition to the other suggestions, make sure fast saves are turned off
(tools -> options -> save -> untick 'allow fast saves'). And see here:
Why are my PowerPoint files so big? What can I do about it? http://www.pptfaq.com/FAQ00062.htm
Like Austin, I've had great results with NXPowerLite. Their newest
version (3.6) is much faster than the previous one. From memory, when
you download the software, you can compress 10 files before you have
to register and pay for it, so you could try it out risk free.
FWIW, I have no association with the company, other than being a
satisfied customer.