So, i managed to connect my N900 to my 4 TB NAS via VPN ans sshfs.
Works fine, as far as the simple networkstuff is concerned.

My Problem is that all Apps on the N900 are designed to work with the rather small internal space, scanning all Media on the Device.
That approach obviously fails when you try to scan about 3 TB data for multimedia files.

What i need is an imageviewer and a musicplayer that works "old school", meaning you have to browse to the file/folder you want to play or view. Like "add directory" in Winamp.