What is your max budget?
Do you intend to do any gaming?
Do you need an OS?
This guy is from the UK (neva) and would know where to get the best deals on hardware over there.
If you build it yourself you can build it to spec with in your budget usually, however you can buy prebuilt around the same price. It really has to do with your personal preferences, and warranty support. Prebuilt = 1 company for all warranty stuff, custom build = tons of different companies for warranty.
I would say build it, since computer knowledge is good knowledge to have.
Hmm cant realy match that site to be honest,they must be using a realy cheap power supply and case in that system...because ive just built a list on ebuyer using quality parts and it comes to £602.51
How this
Intel Core i5 750 2.66GHz Socket LGA1156 8MB L3 Cache Retail Boxed Processor
http://www.ebuyer.com/product/172755
Gigabyte GA-P55-US3L P55 Socket 1156 8 Channel Audio ATX Motherboard
http://www.ebuyer.com/product/174499
G-Skill 4GB (2x2GB) DDR3 1600MHz/PC3-12800 Ripjaw Memory Kit CL7(7-8-7-24) 1.65V
http://www.ebuyer.com/product/180490
PowerColor HD 4670 PCS Edition 1GB DDR3 Dual DVI AGP Graphics Card
http://www.ebuyer.com/product/185912
Seagate ST3500320NS 500GB Hard Drive SATAII 7200rpm 32MB Cache - OEM
http://www.ebuyer.com/product/130828
OCZ Stealth XStream 600W PSU - SLI Ready ATX2.2 12cm Fan
http://www.ebuyer.com/product/127861
Antec 300 Three Hundred Case
http://www.ebuyer.com/product/143854
LG GH22LS50 22x DVD±RW SATA DL & RAM + LightScribe Black - Retail Box With Software
http://www.ebuyer.com/product/190671
That build would probably be better,i think the 4670 is better than a 9500Gt...teh hard drive i chosen has 32mb of cache,the one on that site doesnt mention what cache the hard drive has so it could be small...it doesnt mention what hard drive either!
I actualy think you could get a better AMD Phenom 2 system with that budget,i cant realy see why you would want an I5 system....Intel do tend to be more expensive.
Price out what I built below, most parts are the least expensive for the performace except for the GPU, RAM, and PSU.
i5-750
Cooler Master 590
Gigabyte GA-P55-UD3R
OCZ 700W
DDR3-1333 4 GIG Kingston CL7
VisionTek ATI 5870
W7 64B
WD Black 500GB X 2
WinTV-HVR-1250
HP-2509m
thats a power supply... its basically what gives power to you hole PC.