mpeg layer 3 does not appear in window
 

Hi!
I'm new at this.
I was trying to compress a mp3 file and followed the steps showed at angelfire.com up to the # 13.
Then it all started to go wrong. in the save as window that I have to change the format does not show mpeg layer 3 and does not have the Kbts, hzs and others that i have to insert.
Does any one know what do I have to do now.
My O/S is windows XP.
Thanks.:)