H.264 is usually a good choice. Quicktime, iTunes, and Flash can all play it. Generally a computer will have at least one of those on it.
Well, home computers. If this is for a corprate environment you might have to go with Windows Media. You’ll need to buy a Flip4Mac encoder to do that. THen Windows can see it fine, but in that case a Mac can only view it if they’ve downloaded the Flip4Mac player.
So it comes down to your audience and who they are. Do you want to:
A) Tell PC users to download QT or upgrade to the newest Flash.
B) Tell Mac users to download the free FLip4Mac plugin.
C) Put both an H.264 and a Windows Media File on the same disc and let users choose which one they want to play.
I’d pick a different answer depending on where the discs are going, so I can’t tell you which one to choose.