So, what is it that you're looking for? A solution to use the N900 as a wireless harddisk or as a media device (which, for me, would be mainly music)?

For music / media, MusicPlayerDaemon would be a perfect solution. In my house, all the mobile devices are hooked up to the desktop machine running MPD, and on the N900 that I use daily, MPD runs as well so I can share music on the fly when I am with friends.

Note that MPD is only a daemon to play music. In order to interact with it, you'll need a client. I believe MPC is in the repo's as well as a Qt remake of it.

For sharing things like video, have a look at Knots2.