Thanks for your reply!

You're right for the N800 stuff: I first installed using the "user" branch and after having seen it was a mistake I switched to "user770". Unfortunately, I can't try your command as I already flashed my device to install OS2007 and try xmms on it.

I'll inform you about the installation on N770/OS2007

[edit after flashing to OS2007]
I have problems with dependencies on 0S2007:

The following packages have unmet dependencies:
xmms: Depends: libasound2 (> 1.0.14) but 1.0.10-osso7 is to be installed
Depends: libc6 (>= 2.5.0-1) but 2.3.5cs2005q3.2-5.osso12 is to be installed
Depends: libesd0 but it is not installable
Depends: libglib1.2ldbl (>= 1.2.10-18) but it is not going to be installed
Depends: libgtk1.2 (>= 1.2.10-4) but it is not going to be installed
Depends: libogg0 (>= 1.1.3-2) but it is not going to be installed
Depends: libvorbis0a (>= 1.2.0) but it is not going to be installed
Depends: libvorbisfile3 (>= 1.2.0) but it is not going to be installed
Depends: xmmsctrl (>= 1.9-3) but it is not going to be installed
E: Broken packages