get this
www.dvdvideosoft.com/free-dvd-video-software.htm
Works awesome. Just get what you need to download mp3 off youtube you don't need everything dvdvideosoft has to offer just the youtube to mp3 converter. Believe it or not the download will sound better than the actual youtube. But even better, you now have the MP3 with CD quality. (I recommend using the 320 bit rate)
Look for the best quality youtube of that song. Once you hear something that sounds like good copy, paste the url of it into the window of the program I pasted above. It will download and there you go you now have an MP3 for that song.
I have used this program and technique a lot. Come back and ask if you have any questions.