It wouldn't actually be considered the default mp3 player for LimeWire, but rather for your computer. As it is now than, you have probably inadvertantly told real player to be that default player. Somewhere in the options, you have to tell real player to not play mp3's by default, and than find the defaults in quicktime or itunes and tell them to be the default players. You, of course, can only have one default player though.