Of course you can!
Now follow these steps, I know this may be long, but once you do this yourself, it will be easy.
1) Open your video up in Windows Movie Maker.
2) On the left side of the screen find the section "Publish To".
3) In that section click, "To This Computer".
a) It will bring up a window of what and where to save it as.
b) After doing so, click next.
4) There will be three options, choose the one below:
a) "Best Quality Playback for this Computer (Recommended)"
b) Click that bubble, then click "Publish".
Now your video is published to you computer as a WMV video.
5) Open PowerPoint, and open up your presentation.
6) Once that is open, click the "Insert" tab.
7) Find the icon "Movie", and click the drop down arrow.
a) Within the drop-down tab, click "Movie From File".
b) Find your video file and click open. It will insert it into the slide you are currently on. You can then change the video size, and if you want to auto-play the movie when you change slides, or if you should click the video itself to play.
Hope this helps!
F.Y.I - the information I provided were for the Vista version of Windows Movie Maker, and Microsoft PowerPoint 2007. All the information is the same, and you can still accomplish this task, but the wording in the programs may be different.
If you need extra help, feel free to E-Mail me!