I was faced with this problem when posting some swing dancing videos online. Even though you can use fancier codecs, I decided to go for the least common denominator: QuickTime 3. It works just about anywhere and the quality is "good enough" (although not spectacular).

For some reason, even though I'm running WinXP and I've installed the latest DivX stuff, WMP9 and QuickTime6, I still can't get DivX movies to work properly for me. I imagine other people would have similar difficulties.