Thanks to all for the input so far. Here is where I am currently:-
Intel Core 2 Quad Q6600 G0 SLACR, Kentsfield Core, Socket 775, 2.40 GHz 1066MHz 8MB Cache, Retail £116.20
Gigabyte GA-EP45-DS3, iP45 Express, S775, PCI-E 2.0x16, DDR2 1066/1200/800, SATA II, ATX £76.95
512MB Gigabyte HD4870, PCI-E 2.0(x16), 3600MHz GDDR5, GPU 750MHz, 800 Cores, 2x DL DVI-I/ HDTV, HDCP £173.00
Arctic Cooling Accelero AC-S1 rev 2 Radical high performance passive cooler x4 heatpipes (7950/1950) £15.03
4GB (2x2GB) Corsair TwinX XMS2, DDR2 PC2-6400 (800), 240 Pins, Non-ECC Unbuffered, CAS 5-5-5-18, DHX £63.97
Scythe Ninja II Heatpipe Cooler, with 120mm fan + Zalman FANMATE 2 Variable Fan Speed Controller £40.00
520W Corsair HX Series Modular PSU, ATX, EPS12V, whisper quiet £69.31
Total of £554.46 (works out less than the original spec)
I already have the Antec P180 case & 24" Dell monitor.
The only thing here I am unsure of is will the GPU cooler fit the HD4870 as it looks pretty sealed up on the picture. And, will it be sufficient to cool it?
Edit> I also consider to upgrade to the 300 GB Western Digital VelociRaptor as a main system drive. I also hate waiting for HD's and I know it's expensive but someone with my patience would understand it's worth the investment