hi Tony
Firstly let my agree with the previous replies who recommend the squeezebox.
18 months ago, when all available shelves were finally full I decided to rip all my cd's to a hard drive and bought a squeezebox duet to stream the files to my stereo. It was the best buy ever. Ripping 1000+ cd's was a ball-ache, but my living room is so much nicer now that they are all gone.
The squeezebox duet has the best interface for selecting music and as a bonus has access to various online streaming services for new music and internet radio. It has really changed how I listen to music. The sound quality is also excellent, easily on a par with standard budget cd players (eg rotel, arcam, etc) and of course can be attached to an external dac if you have magic ears.
Get one. They are fantastic. Although waiting 'til xmas for the touch version might be worthwhile (easier to set up). The main consideration for me is how to connect your hard drive music to your existing stereo with good sound quality and without having a pc in your living room, the squeezebox is just the ticket for that.
Anyway the most important thing to consider is what format to rip to, what program to use and so on. This all depends on how computer savvy you are and how hifi obsessed you are. I ripped everything to flac. Sound quality wise mp3 at 256kbps was indistinguishable for the majority of music but flac is more flexible and future proof, allowing re-encoding to other formats (for ipod etc) with no great loss in quality, so worth it for me,
Anyway - check out the squeezebox forum for endless information.
Also consider sonos, or a mac based set up with an itouch controlling.
Good luck with it.
Ant