Well, given that you're in the UK and don't have the means to build it yourself, I guess you're only left with Dell.
I did a quick look around at the Dell & Alienware UK website.
It seems like in the US, the Small Business Section charges less for the same thing. And the same goes for the Alienware site, where a similarly configured Dell is about 200-300 less than from Alienware.
Anyway, if you're a gamer
get this and configure based on your needs.
My advise is to get it configured as follows:
Q6600
2GB RAM
320GB (2x160GB) RAID-0
16x DVD+/-RW
Nvidia 8800GTX 768MB
Worthwhile Upgrades:
16X DVD-ROM so you have two drives
Creative X-FI Sound Card if you don't want to use the onboard
Anyway, the base price is 949 and the upgardes will push it over 1000.
AS for why only 2GB, well RAM is easy to upgrade so if it proves insufficient when Crysis comes out then you can upgrade and usually do so for less money than from Dell. With the Video Card, it's one of the best out there with the exception of the 8800 Ultra. If it proves insufficent, I believe this board is SLI ready so you can stick a second one in there for more performance or you can see what's out there a year from now and upgrade to a different card alltogether.
I would also get a second hard drive for storage. Dell apparently only allows you to configure this system with RAID. So it's either two 320GB Raid 1 for extra money or two 160GB for the above quoted price. It's up to you which to use. For speed, Raid 0 is faster, but should one drive fail you're screwed since your data is striped across two drives and thus if 1 is broken, you only have the other half which is unreadable without the other half.
Anyway, as for the processor, I figure that if it proves insufficent you can always upgrade the processor later for again less money. If you want to overclock, then I'm sorry you're kinda screwed in that department unless you can either build it yourself, find someone to build it for you, or pay extra money from Dell/Alienware to get an overclocked system which defeats the purpose of overclocking to save money.
Oh and as a final note: to give some comparison, a similarly built computer is around $1350 US.