You can use iTunes, but that's not in mp3 format. I believe that Amazon is though. You could also just go to the store and buy the CD, those are in mp3 format.
Copy URL of a video from youtube and paste it on youtubehack. Then you choose what format you want. But... It takes long time and not that good quality. Then use www.tobbeno1.se. Then press "Musik". A swedish site but good. maybe you can change language there,i dont remember :P