I assume there’s some program out there but I want a legal, free one. I have some music videos where I want to reuse the music and sound in other videos but I don’t know how to get just the music instead of the music and video. These videos are in .flv, .avi, and .rm (realplayer) formats.
You could use something like this: Pazera Free Audio Extractor - Free download and software reviews - CNET Download
I can give you some names if you want but a more general guide for all such needs is to go to www.download.com which is run by CNET and very legitimate. It has editorial and user reviews of all types of shareware, freeware, and payware that you can read about and get instantly plus a search engine. I have a few free programs on my computer that can do what you want but it is probably easier to use their search function to pick the free one you like the best. Use the keywords like “rip” “audio” from “video”.
It works! Wow that was easy, thanks guys! 
I’m well on my way to being the next Spielburg! Or Michael Bay, whichever.
I always use the converter program that comes with the free version of Real Player.
Going to the download cnet.com center, you actually can find a lot of software for ripping mp3 from video directly. You can use programs to record mp3, wma audio files from videos in any format. Also, other tools with converting functions can help you rip audio. Otherwise, search keywords on engine and find a good tutorial.