MPlayer normally just returns. There's no GUI. Did you try running "mplayer somevideo.mpg" or just "mplayer"?
Of course I did both plus mplayer --help, mplayer -h, etc.
Same result.
I also found out that most players in Jaunty segfault or end up with an illegal instruction, including audacious, totem-xine, etc.
Btw, the upgrading way (apt-get update, apt-get upgrade/distupgrade) did not work as it left me with lots of unresolved dependencies and a cyclic dependency in libc6. So I did a fresh install. To make lxde work as before I had to replace icewm by lxde and uninstall the gdm login manager- which did not let me login as root and there had not been created a user account before.
Another issue: adduser leaves me with a user account which is not allowed to do networking as ping, nslookup, etc. all return with an error.
The new user has to be moved in a certain user group which I am actually not aware of.
Besides this jaunty looks to be a bit faster than hardy and being able to test drive fennec is worth the installation effort.
Oliver