Generally, there are 3 things you need to know when building a mining rig.
Graphics Card: This is what is actually going to be generating your coins so don't be cheap when buying a GPU
Power Supply: You will need decent power to run your rig so if you are getting 2 or more graphics cards, don’t get anything under 750w. A good one for this is the SeaSonic X Series X-850.
Motherboard: The only thing you need to look for here are the amount of PCI-E slots (or places for your video cards). Try to find one with at least 3 slots so you can expand if ever decide to. A good option is the ASRock 970 EXTREME3
Putting it all together can cost between $800-1000, depending.
In terms of software requirements, you'll need to consider these:
Mining software, such as:
CGMiner
Poclbm
Phoenix Miner (Linux)
DiabloMiner (MAC OSX)
Graphics card:
ATI card recommended
Coin Wallet:
The wallet that is specifically for the coin you are mining
Once you have it all set up, here's a link on what to do next:
http://bit.ly/MiningConfigurationIt's a lot! But if you're committed, you can do it. Exhaust your resources, and good luck!