You can easily download videos from YouTube and Google and use them in your PowerPoints. You can go to other video sites too, although the millions of videos available on YouTube should be enough to enliven your presentations.
These two programs are inexpensive and easy to use:
PC: Use Quivic for $14.99. Free trial download.
Mac: Use Tubesock for $15. (They now have a version for the PC too but I haven't tried it.)
After downloading you can edit the videos on any video editing program - even on Windows Movie Maker or iMovie which come for free.
These are the simple instructions - read on for more advanced conversions to iPods and other displays...