Building a cheap gaming computer is just like building a regular computer. Only, it will require you to have a good graphics card and a lot of ram. Here are the parts that you are going to need:

1) First of all you will need to get a case with a power supply. Most come with power supplies built in.

2) Motherboard is the next thing you are going to need. Don't spend too much money on it. They have some good ones for a really cheap price.

3) Next thing is your processor. A lot of people argue, which one is better. Intel or AMD. I would say that they are pretty much the same. And if you are going for the price, then AMD ones are usually a little bit cheaper.

4) Graphics card. This is a huge part of your gaming computer. The bigger memory your card has, the better. I would say for Nvidia, the best card out right now is Nvidia GeForce 9800. But if you are looking for a cheap one, GeForce 6600 should do the job.

5) Ram. Ram is also a huge part of your gaming computer and again, the more ram you have the better. I would say go for about 1GB of ram. That will be fine.

6) All the rest is the parts you should know of like a mouse, keyboard, etc.

The specs that I gave is this article will give you a pretty good performance on any game on the market right now. On high or mid setting, you will never again experience lag.