Michele is right. I have a friend who sends me Powerpoint files once in a while. I've tried to tell him, I can't open Powerpoint files, 'cause I ain't got Powerpoint.
There are some formats that are a safe bet, because almost everybody has the software to run it. MPEG files are pretty universal. So are Flash files (Flash would be better for what you're doing). You'll have plenty of extra space on your CD, so you can include a copy of the Macromedia Flash software in case they need it. There are no limitations on distributing their free software (but double check).
If you have good tech help from friends, set it up so that it will automatically start when the CD is inserted in the computer. Also try to make it so that it will automatically run at full screen instead of a little window. Don't ask me for help with this, because I wouldn't know where to start
