Buying a desktop computer in the UK (games, monitor, import)

[skippy upwood]

I live in the UK and I'm looking to buy a desktop computer, since my current computer (which I bought in 2004) is falling apart.

My monitor and speakers are in a reasonable condition so I don't need to replace them.

My criteria are:

- Must be £500 or less

- Good quality components, esp. a good cooling system - I don't have A/C in my study and its gets dusty at times.

- Reasonable customer service

- Up to date, since I enjoy playing computer games.

Any recommendations (other than self-build and importing from the US) would be very welcome.