Anyone know how to do this? Need YouTubeish help

[annearchy]

I'm trying to make a video for darling daughter. We've got an animation (downloaded from YouTube, where the videographer has it up and available so people can do remixes) and also an MP3 to use as background music. I used Total Video Converter (a great software program I got from one of my music buddies) to strip out the audio from the animation. I'm using Windows Movie Maker, which came with my Windows XP, to add the audio to the video. I've even got the audio aligned so that it doesn't start until after the title slide and a few seconds into the video, just as DD wants it. I've saved it several times to my hard drive as a .wmv, which is what Windows Movie Maker does. When I play it back in Windows Movie Maker the sound is there and the music sounds just the way we want it. BUT - when I upload the same file to YouTube, there's no sound. WTF??? Anyone know what I'm doing wrong? Feel free to ping me on YM (montiac712) or leave a comment here. Gah, so frustrating.

Oh, if you find there's no icons in comments on my LJ, I've turned off icons (except my own) to try to avoid Deathly Hallows spoilers. Yes, I am paranoid :P