If you feel that you can't make your own movies you can still use other people's. There is a lot of good stuff out there if you know how to use it. YouTube is a good place to start. Most of the links on this site are to YouTube movies.
YouTube is a great source of inspiration with lots of movies which you could use yourself. It is easy to download them and run them as stand alone movies or from within a PowerPoint presentation. The easiest way now is probably to use Real Player. This is a media player capable of replaying a range of formats including the proprietary Real formats. I'm not that keen on it and it has one annoying feature which you need to be aware of: from time to time you will get a popup advertisement on your computer inviting you to speed up your computer or upgrade the player. You can just close these when they appear (every couple of weeks or so) and they do no harm other than mild irritation.
But the big bonus of the latest RealPlayer is that it enables you to download nearly every movie which you find on the internet (it is possible for a site owner to block downloads). This mean that all Youtube, Google Video and many other sites are available. You will normally see a 'Download this Video' window at the top right of the screen. Just click on it and the video will download to your computer. You will also see a little arrow; clicking on this activates a drop down menu enabling you to 'Save As...' and set default preferences for the program.
Once the video has downloaded (normally in Flash .flv format) you are offered the opportunity to convert it to another format. There are better format converters around but this is good enough for many purposes. You are offered the choice of conversion to a number of different devices. I recommend setting up your own 'device', called, say, "Windows Media" by customising the XBox setting. If you set the format to Windows media; the Quality to 15Mbs (High); Resolution to 720p; Audio to Windows Media Audio; and Quality to 256 kbs Stereo you will have a reasonable quality .wmv file which you can run from within PowerPoint.