It seems that xmms cannot play music when ESD is enabled. Xmms gives an error message, saying that the soundcard is busy and the user should make sure no other applications are blocking the soundcard.
If I turn off ESD, xmms can work properly. Is that a bug of ESD? What should I do if I want to have system sounds (System->Preference->Sound->"Sounds" tab) and at the same time being able to listen to music through XMMS?
FYI, this is the configuration of my laptop: Lenovo IBM T61, Debian with kernel 2.6.22-3-amd64.