if you are looking for a way to defeat the digital rights protection on music i'm afraid i cannot help you. if you have purchased music from a site like itunes or rhapsody you would have the license to play the song.
The answer I provided allows you to pull down codecs that will fix many software based issues with playing music thru windows media player. You still need to license(s) to play songs distributed over the internet.
Songs MP3 format do not have this DCMA protection. this is the only site I know that sells popular music in this format. i'm sure there are others.