can't lauch songs while downloading need help!

[marron5]

I downloaded windows media player 11 beta, before I downloaded this I could launch music from limewire while it was downloading, but when I downloaded windows media player 11 I did something wrong. I used windows media player 11 as the standard player. before I had winamp as the standard player,
now when I am trying to lauch the file, it pops up a message. written: this file isn't recognizes, you can't play the file.
What can I do to lauch the songs while I am downloading without getting the message. I can't listen cause it says that it isn't recognized, before I could with winamp. How do I change standard player and how can I lauch songs while downloading?
Can somebody please help me?