http://www.xvidmovies.com/codec/

I hope you saved an uncompressed version of your video else you'll end up with some awful artifacts.

Save the codec, install it, use it in virtualdub or whatever program you use to reencode your video.

There's several other codecs than the one I listed. You can try all sorts, like the latest divx(which you have to download the player with to get the codec), huffyuv, lagarith.

Really, what you ought to do is take some time and peruse the forums and files at http://www.animemusicvideos.org