A price budget for components would be a bit more helpful.
Basically you'll need:
a 5.1 sound card like the turtlebeach santa cruz, live 5.1, or audigy
Then a 5.1 receiver with around 100 watts per channel. (many to choose from)
Speakers:
If you want some good quality speakers and not break the bank, I'd look at the JBL Studio series with S38 bookshelf and S center they sell at
crutchfield. Those sound real nice, I've also heard a Klipsch with KSW-12 home theater that sounded nice as well.
Then buy a subwoofer like a highly acclaimed
svs subwoofer like the smallest self powered PCi. Or you could stick to the same brand for all your speakers for tonal matching. (center channel matching front towers are important to match)
You'll hook the sound card to your receiver with a digital cable, and the receiver to your speakers. If you have a video card with component out or s-video then just plug that in a tv. There are other options like hooking your speakers to your subwoofer, and hooking the sub to your receiver... but you should play with different configurations when you have a manual sitting in front of you.
If you have some more money to spend, you may be interested in a higher line of speakers such as Paradigm studio/monitors or Diva Swans. Those speakers can go for over a grand a pair. If you decide to go all out, you may be interested in buying a pre pro like the new Outlaw 950 ($900). Since you'll need an amp you can go for a 2 and 3 channel amp as it probably would have better headroom. Or use a 5 channel amp that is essentially 5 monoblock amplifiers in one chassis(such as the Proceed Amp 5). Another possibility if you are contemplating EX type surround is to get a good 5 ch. amplifier(like a Parasound 1205) and a killer 2 ch. amplifier. (katbamna)
Before you think about building a home theater I suggest you register in hometheaterforum.com or avsforum.com and have your questions answered there. I do warn you that it will probably cost you a lot more money once you learn more about the hobby. You may also end up acoustically treating your room, hiding cables, and tuning complex equiptment so it helps to be a handyman.
Actually today I spent hours of just listening to music on an expensive home theater... I just sat down, closed my eyes, and braced myself for the goosebumps.