The best place I have been for this type of info is Audio Asylums PC Forum. There is a very active and knowledgeable group there. You should do some searches since questions like this come up every day. You can find my posts under xmasparty
http://www.audioasylum.com/forums/pcaudio/bbs.html
I find that it is helpful to break the problem down into two parts.
The first part is using a PC hard drive instead of a CD player as the transport. There is a huge benefit to this in that all the jitter associated with CD playback is eliminated. No more complex electro mechanical optical transport spinning imperfect discs in real time at varying speeds. Eliminating the CD player is the biggest single performance improvement.
Using a hard drive as your transport, you are pulling relatively small quantities of data off a drive with full error correction - keep in mind that to a computer audio files are very small and easily managed. You will however need a lot of inexpensive storage, and the discipline to back the drives up.
Ther key to quality is how you encode the data (rip) to the disc. The only satisfactory solution for an audiophool is either in .wav or .aiff or in a lossless format. iTunes and EAC are the premier tools - iTunes is crossplatform and offers a very high degree of integration. EAC is freeware, PC only and has a steep learning curve. There are plenty of people who are happy with each. Some people do .wav but as I understand it there are issues with file tagging (naming) Plenty of info on this on Audio Asylum
Part 2: Now that you have your music on the hard drive, you need to get it to the preamp. There are two things happening here. One has to do with the software that lets you select the music, make playlists etc. We won't touch on that - there are a number of solutions available, iTunes being the most highly integrated and easiest to use.
The big issue for most people is how to get the data from the hard drive to the preamp inputs. There are a number of choices:
#1 - you can put a sound card in your computer and output an analog stereo signal and send that to your preamp. This is almost unanimously considered to be the worst possible way to do it since computers are nasty electrical environments - lots of EMI and RF, switching power supplies, fans etc.
#2 - you can take data off your hard drive and send it to another device using USB, Firewire, Toslink, SPDIF, 802.11g (WiFi) or Ethernet. A few notes here:
SPDIF smear is the number two culprit you are trying to eliminate (thus the USB DAC) Besides which practically speaking a premium SPDIF cable over 6 feet is brutally expensive. Since you need a soundcard to provide the SPDIF out, you are back to ground zero - plus the DAC is not isolated from computer - more bad. And since SPDIF is not a computer format, it will never be ubiquitous or cheap since PC buyers don't care about it.
USB is an excellent format for taking data off. There was a wonderful, inexpensive device called a Waveterminal which let you plug USB from the PC into a little black box on the other side of which were toslink and SPDIF outputs to connect to the DAC. Unfortunately it has been discontinued so people are trying a variety of products instead.
A very fine high end solution is a USB DAC, which as previoulsy noted eliminates the need for a SPDIF output and connection. The only downside is that a USB cable goes 15' max - so you have to be willing to have the computer in your listening space.
Firewire - there are a few devices using Firewire, no real market acceptance. Firewire will go to 30' with a repeater. A lot of people are using Firewire to run their external hard drives for their libraries and backups. Its good but if you can use SATA its much more robust and its faster.
Toslink - I run a premium glass Supernove 15' from the built in output on my Mac G5 to my DAC. Works very well, much less expensive then a SPDIF of the same length and immune to RFI etc. Of course the Toslink has to be well implemented but I prefer it to my USB>Waveterminal>SPDIF. YMMV
WiFi - 802.11g This is the wireless standard that Airport Express is based on. Squeezebox also is available this way. Results vary - it is totally environmentally dependent. Tough to beat the convenience though.
Ethernet - this is the low cost, long distance ubiquitous cabling champ. The premiere device taking advantage of it is the SLIM DEVICES Squeezebox. This is a network device - meaning that it plugs into the Ethernet network just like a computer, printer, router or anything else. This is particularly nice if you have a network (Ethernet or WiFi) connected to the Internet - now you can stream radio without using your computer
To use the SLIM, you install an applet on each computer on your network that has music you want to access. SLIM provides a browser based interface that is organizationally similar to iTunes; as well as access from a remote using the display on the device. (The WiFi version works the same way)
This means that the computer need not be in the same room as the system. Very convenient if you want to support multiple listening areas with a common library. Also note that the SLIM browser can share an iTunes Library - so for instance I can use iTunes to rip and manage my library, iTunes with a DAC in my office, iTunes to support our iPods, then SBs in the bedroom and living room.
There are at least two companies, Bolder and Red Wine Audio who are doing mods for the SB2 and SB3 at very reasonable prices ($400-600). The resulting quality is nothing short of astounding and is delighting everyone who is trying it - myself included. Just a matter of time till someone publishes a shoot-out between the modded SBs and the USB devices. My guess is that unless you have an extraordinarily high quality system you will be happy either way.
Last week, Steve Jobs announced that Apple had sold 14 million iPods in Q4. This means that as more and more people want to use the music they have gone to the trouble to rip; more and more companies will offer ways to do so.
But get your feet wet now. You will be amazed at how good the results are and how inexpensive it is.
Here is an excellent blog on the subject
http://musicserver.blogspot.com/
And here are the writings of a very knowledgeable modder - Steve from Empirical - on the benefits of this approach
http://www.positive-feedback.com/Issue22/nugent.htm
Here is a review of a SB3
http://www.enjoythemusic.com/magazine/equipment/1205/slimdevices_squeezebox.htm
Finally Srajan has started covering this and had a good kickoff article recently you can find at www.6moons.com
http://www.6moons.com/industryfeatures/harddrive/harddrive.html