To build a good audio PC, you really need a system of pieces that work together. Here's what I'd do:
Get a small or unobtrusive PC that's very quiet. Run XP and use Foobar for playback. The PC hardware needs 500M+ of memory and a 2GHz processor max. I'd use a 200M hard drive... or whatever the operating system will run. The most important aspect of the PC is that it has a good (bit perfect) digital out (unless you are using a USB DAC). You'll also need a monitor to place near your listening seat. Leave some slack, get long cables. A wireless keyboard might be a good idea here... but wired works too.
$~500
Strip it of all software you can, run the minimum services required to be a networked PC that can play music.
Clean all connectors, ethernet jack, usb ports, etc. with some CAIG and lint-free applicators.
Use new, correctly wired ethernet jacks and cabling for your wiring. I do not use wireless. It sucks for audio quality in every test I've done... and it's unreliable, slows down my network, etc.... So, I'm going all wired for the whole house.
$~20
Use a good switch or router
$~300
Build a music server with a good processor and memory by today's standards. Use 2 1-TB hard drives. Or, start with 1, whatever you need plus 50%.
Put EAC on the server. Use the server to burn your cd's with the correct offset and for the best drive for CD-burning. I recommend a Plextor CD-RW, not a DVD combo. This can be in any room but the audio room... too noisy... needs air movement.
$~900
Load up all your music to the big server in .flac format. Create an automated backup for anything that changes to your NAS. The server is where all of your music will be. If you have the Squeezeboxes, load it on the server.
Oh, buy a NAS that's as big or bigger than the PC's storage. Good ventilation needed for this too.
$~300
All said and done, you're talking 2,k to setup a long-term excellent-sounding 'transport system' including backup and playback for your audio system. Add your DAC and start listening.
This is a lot of work to put together correctly. Luckily there are plans to get this done.