A computer build for me

Hey there!

To put it frankly, I'm somewhat clueless about viable builds for computers as I've never built one before. I have no idea which components are the best, which bargains I can take advantage of, etc, so I thought I'd join up with the site and ask for advice and opinions about potential builds. I've done a fair amount of research into self-made computers, so I'm fairly competent with my terminology so no need to worry.

I'd be extremely grateful if the general community could use their computer know-how and experience to formulate a plan for which components I'll purchase based on these preliminaries:

1. A fairly high spec computer with a mid-range or better graphics card- The main purpose of the computer is to fulfill the demands of modern online games such as Tribes Ascend or the upcoming title Guildwars2.

2. A budget of anything up to £550 (I'm sorry, I don't know what that would be in dollars; that's British pounds by the way)- If it turns out I can afford to pay less, by all means mention it!

3. The components much be available for shipping to the U.K- If you can't tell, it's not that important as I may still be able to source them somehow.

You can safely assume that I haven't got any parts already, but don't worry about the monitor, I have that sorted already.

Yup, I think I've covered everything!

Thanks in advance