How different are WMA and MP3?

WMA and MP3 compress audio files differently so they have a reasonable file size to put on a computer or music player. mp3 is the "industry standard" audio format, in other words it's the most commmon. It's been around since about 1980. wma is mircrosoft's audio format, and I think it's only been around for a couple of years. Microsoft claims that if you compress an audio file using mp3 format, you can get the same quality compressing it w/ wma, for only half the size. In other words, wma is twice as good as mp3. It has been debated whether or not this is true. Another thing to add about wma is that it is generally the format of songs that available from online music stores (napster, yahoo etc) although not on itunes.