Despite earlier messages saying The Sims 2 will save uncompressed AVI video files when creating a movie, it has turned out that EA has licensed On2's VP6.2 codec for use in The Sims 2. That means movies created from The Sims 2 will need that codec (a little sort of 'program' which media programs use to decode the video files) to be played. On2 claims that their codec provides better video quality than Windows Media 9, Real 9, or H.264. You can find the trailer of The Sims 2 on the VP6 samples page. It's very likely that the necessary files will be included with the Sims 2 when you install it, so there's not really a need to install the codec already. However, you can of course go ahead and get yourself ready to play Sims 2 movies in the future.