Alright, this one is driving me nuts. I thought that it would be a quick and easy fix, but i was wrong. I have lame installed, and mplayer, and mencoder, and yet it continues to say that message. I reinstalled lame, updated my path to include /usr/lib64 and /usr/local/lib64 and did a source ~/.bash_profile, and whiched the lame and mplayer binaries again, and the libmp3lame.so.0, and it all shows up. I reinstalled mplayer and mencoder after reinstalling lame and ffmpeg and lame-devel. I still get that message.
I know that there is an option to -enable-mp3lame when compiling mplayer -- but i don't compile; if i can't yum it, then i won't use it (to ensure compatibility, etc). I never had to compile it before, but i haven't transcoded to Xvid format since fedora 9, as i only use x264, unless there is a special need, which there is now. Anyway, like i said, i'm stumped. I've never had to compile mplayer before to use the mp3lame option, and i'm sure that there is a way to get this working on F-10 without manually compiling. Googleing didn't help.