Go computer geeks! I'm one too, so welcome brother. First things first, you'll probably want to grab a copy a Windows Media Center. Now, I must say that I don't have experience with it, but considering its purpose, I think it would be the best way to go.
Second: go the digital route. Your computer's sound card (onboard or separate) probably has garbage D/A converters (digital/analog). Any good quality reciever or preamp will have good, high-quality converters that you should take advantage of. The best way to do this would be to use a TOSLINK optical connection or SPDIF coaxial connection. Both are digital options and can be found on most computer audio products. Plus, digital can transmit all 6 channels of surround sound with one cable, so you can have all the gaming goodness you desire!
Third: Don't waste your money on Monster Cable! It's just a brand name. There are many other cable products that meet or exceed the quality of monster for much less money. Unlike computer components where brands really matter (I shudder to think about the bad mobos I've played with), audio cables don't need the flash. Of course, this doesn't mean you should just be using the cheap cables that come with your components. There are great companies where quality cables can be had for good prices. These include
Blue Jeans Cable,
Ram Electronics,
Impact Acoustics,
Cobalt cable, and
River Cable.
I'm not really sure about programs. I would think that any media player will work. However, assuming you get some quality speakers, you will notice that 128kbps mp3s sound horrible. You're going to want at least 192kbps. Still, you'll be finding that you gravitate more towards CDs and lossless codecs on the computer.
Well, that's all for now. I hope this helps you.
Lastly, welcome to Audioholics!