I totally agree with locke, building your own PC is almost always the best option: you get to pick the exactly configuration to fit your needs, it will cost less (or you get a more powerful machine for the same money) than buying a prebuild and often the warranty of the individual components is longer than the warranty a company will give you for the entire machine - so you can get free replacement kit for longer if you build yourself.
The main barrier for building your own machine is knowledge and confidence. For knowlegde, having a read of PC building threads/guides around the internet (
this one by greywolf is excellent) and checking out detailed instructional videos on youtube is the best way to acquire the knowledge you need. As for confidence, this will come after acquiring all this knowledge and asking fellow enthusiasts about their own PC building experiences. If you have any questions at all, please feel free to post in the relevant sub-forum on OCUK and we will all be happy to give you a hand.
I would be happy to spec you up a set of componenets for an excellent gaming machine to fit in your budgett, but may I first ask you a few questions:
- Will the machine mainly be used for gaming, or will it be used heavily for other tasks too (eg movies, photoshop, CAD, disributed computing, video editing etc.)?
- Do you need any peripherals along with the main box (eg. monitor, speakers, keyboard, mouse, wireless adapter, gamepad etc.)?