Got mplayer working well in PowerPC (G3, 600MHz), with the new ffmpeg. I had to use -ao sdl to get it working. The video wasn't as smooth as with -ao null, but it was OK, at least. I am under the impression that using -vo sdl:x11 is better than using -vo x11, at least with the Rage Mobility 128. BTW, it was also possible to play DivX 5 movies with this setup (the new Star Wars clip).