there's a version 0.9x? that's news to me!!
in mplayer you are looking at the list of formats that mplayer can decode. This is totally different the the formats that MEncoder can encode. you will have compiled mplayer without mp3lame support, or installed a version without it already in it. when you run acidrip from a terminal you will be told loudly that there is no mp3 support.
run this "mencoder -ovc help" that will list the formats your mencoder can use, and this is the exact way acidrip finds the list out.
btw, new version out so so soon. maybe this afternoon... maybe.