If you want a PC for gaming on the cheap building your own is the way to go. If you don't want to actually assemble it yourself there are services online that will assemble it for you for a small fee. You should also ask around your mates and see if they have the know how to build a PC and see if they could do it for you.
When buying a gaming PC the thing you want to look for is the CPU and GPU. When looking at CPU's look at the model number, not the clock speed. A 1.5GHZ I7 is much better then a 3.5GHZ I3 for instance. With GPU's your looking for a mixture of processor clock speed and memory clock speed, you can pretty much ignore how large the memory is as its kinda irrelevant. Everything else doesn't really matter, but you want to make sure that nothings bottlenecked so you get the most bang for your buck.
You want to make sure that it'll last you a couple of years so it's worth forking out a couple extra hundred then having to upgrade most of your system in 6 months. Also something to keep in mind is that while the initial cost of a build-it PC is a tad expensive once you've built it you only have to upgrade one part at a time, meaning you don't have to go out and spend lots of money at once.
I know this can sound kinda overwhelming but it's worth knowing. The more you know the better deal you can get.
The most important thing to remember though is to do your research. Take your time, ask around on forums and review sites and never buy HP or a Mac.
EVER...
