Unfortunetly, I am not at home and have no Linux PC(Can't even try on n800, cause I send back my SD card today), so I can't give you mplayer output right now. But the -ao esd -ac ffmp3 parameter worked when I tried tonight. The problem is that the performance got very bad with this option, even while the cpu ist just 3/4 of maximum (2/4 when without -ao esd -ac ffmp3). Isn't mplayer using ARM Core for decoding, so cpu should be 100% in use? Or did I misunderstand something? Nevertheless, I'll have my Tux back soon (And hopefully a new working SD card) and I will post outputs.

PS: The movie worked good in every other windows player(WM,VLC) and Linux player(mplayer,vlc) I tried...