Thanks Steve! I've made some progress.. Kindly review my new proposed sys:
MOBO: MSI P35 NEO2-FR - £66.46
CPU: Intel Q6600 OEM - £150.27
CPU COOLER: Arctic Cooling Freezer 7 PRO - £14.63
RAM: Patriot 2GB PC2-6400 C4 Extreme Performance (2 x1GB) - 35.19
GFX: ATi Radeon HD 3850 512MB PCI-E2.0 - £105.69
CASE/PSU: Antec Sonata III with 500w PSU - £75.14
TOTAL - £519.02 inc. VAT
My only concerns are with the stock PSU (I mightadd a Corsair VX 450w) and the GFX card... 3850 isn't amazing, but the machine is ready for CrossFire should I need it..