Needed an app for this. Maybe someone else has use for it too. I may add some new features later (like video), but don't hold your breath. Won't probably work with AppleTV, but if someone wants to donate me one, I'm sure I can make it work too.

Requires XBMC 11 (Eden). Make sure you have bonjour/avahi installed too. Enable airplay under settings -> network. Don't setup a password.

Install attached package to your N900. Run apt-get -f install as root afterwards to install all required dependencies. Needs packages from -devel/testing, so don't install this if you are afraid of those.

EDIT: may require a reboot or manual start of avahi after install.