There's no easy answer, so you'll be lucky to get much help. The link above is one of the best, but if it doesn't work . . .

good luck getting the movies to play. Until a clear winner emerges, the video codec war means headaches. Players have to have the required compressor/decompressor ("codec") used to make the movie.

Here's a Quicktime link that will allow you to play some movies:
http://docs.info.apple.com/article.html?artnum=30506
This also points out that some movies will play in OS9, but not OSX, and vice versa. Joy, eh?

search the forums for "software component could not be found"--lots of complaining can be found, as well as a few solutions for some movies.

As others have pointed out, search the net for "vlc" --this awkward little app plays most movies--even the mangled and partial ones that end up in your Limewire incomplete folder.

Do us all a favour: if you find a comprehensive solution, post it here.