I've been looking at this kind of stuff as well and short of spending a small fortune on a fireball - I've found this;
[Link: apejukebox.com]
It runs on any PC and has a very slick interface. I manage/rip stuff in MusicMatch Jukebox, and intend to play with ApeJukebox, and modulating the video signal to all TV's in the house, while feeding the audio to the whole house audio system.

My problem with the dedicated units is that they are out of date as soon as you buy them.

I'm still searching for the ultimate media server which will allow full video and audio from the one interface.

Good luck