I agree with C64, except I think the Arctic Cooling Freezer 7 Pro should do the job and save roughly £20... Also, don't get the 8800GT at all costs, it's last gen stuff. You definately want a very strong PSU, not a high watt one, that's not important. In my opinion the things to look out for on a PSU are
1) Single 12v rail
2) If you can find out (I know Ananadtech test for this) then you want one with very low oscillation in the power output of the rails (i.e so that the output is cleaner)
3) Also you want the rails to run as close to stated values as possible
4) Also look for a high efficiency supply... they have an 80+ rating I think... high-efficiency, while it does translate to power bill savings, I'm recommending it because it generally means the PSU is very well built and tuned.
5) Something most PSU's have these days, a 120mm fan on the bottom and an "open" beehive style back (basically a mesh/net/perforated back). This will help with case airflow.
For the CPU, pick the slowest one that has the normal cache... I wouldn't really go for those cache-reduced versions (i.e. Pentium Dual Core). I wouldn't bother with wolfdale or quad core either as C64 said. I got my Q6600 back in November/December when they were new-ish... now I bet something better is about to come out so it's best to wait and stick with a basic, but good CPU.
The case. Pick something with a 120mm intake (preferably) at the front and a 120mm exhaust at the back. If it has an exhaust on the top of the case, then that's all the better for you. If not, then don't worry. I don't think all this business about side vents/fans is that great to be honest. Personally I like just a 120mm quiet fan at the back of my case, I wish I had space for one at the front too! There are cases with freely perforated fronts (or at least, bottom of front) a bit like the Powermac/Mac Pro from Apple and these generally can take 120mm fans, that would be your best bet. Make sure it either comes with a dust-filter, or just cut one and fit it yourself. It helps.
If you're up for it, replace the northbridge/southbridge thermal tape/whatever (these days they use this hybrid between paste and tape, not sure what they call it) with some Arctic Silver 5. It will lower temps a little. If you can then get a mini fan installed on your northbridge too, because by the looks of it, if you get a processor with a low multiplier, you're going to need to run that northbridge pretty hard.
RAM isn't that important. I guess we're spoilt for choice these days with RAM. I'd go for the OCZ PC6400 DDR2 sticks, they're cheap and OCZ's service is very good. But that's personal preference really.
Choose your own Optical Drive. If you only need it to install windows etc like I did, then any cheapo one will do. Just make sure it's SATA, it'll make your life easier

Oh actually, SATA Optical drives do sometimes have issues with Linux from my experience, but otherwise they're lovely (good riddance, old IDE cables!) Also maybe spend the extra few pounds and get a retail one if you can. I did that, gave me some peace of mind (some might say it's a waste of money though).
Hard Drive, don't buy a raptor lol. I bought one even though I KNEW I could get more storage for a lot less cost, and just a little less performance, but I guess I just wanted to be able to say "I've got a Raptor"... sounds cool eh? lol ok seriously, maybe in their initial days Raptor's were all the buzz, but now with all the improvements to the normal drives (i.e. SATAII, NCQ, bigger caches, etc although I'm not sure how much difference each of these features make, but they seem to have overall made drives quite a bit faster) it's not really worth getting a 37GB Raptor anymore. The 74GB Raptor is even starting to lose it edge and the 150GB one is way too expensive.
Basically, the main rules to be follow here are: make sure you have a motherboard which can take high FSBs with ease, make sure you have a very strong PSU as I described and make sure you'll be comfortable with your case (i.e. noise). Get a new generation graphics card and get a basic CPU and overclock it.
Hope this helps, and welcome to the forums
