£600 to spend on first build need reccomendations

I really would not use that power supply. This is probably the cheapest one I'd for to power two 5770s: OCZ StealthXStream 600W £50

Would you mind answering some of the questions posed in this thread: http://www.tomshardware.co.uk/forum/261222-13-build-adv... As any suggestions could be rendered useless if someone doesn't know what's required.

what would you suggest to power 2 5850s?

A good 650W PSU or one with around 600W minimum on the 12V rail, would be my recommendation. So any of these:
http://www.tekheads.co.uk/product/Corsair-TX-650W-ATX2....
http://www.tekheads.co.uk/product/OCZ-Z-Series-SLi-Cert...
http://www.ebuyer.com/product/191826
http://www.ebuyer.com/product/159920
http://www.ebuyer.com/product/161664

Dont get disappointed if you end up with a dual core. Its a risk, the other two cores might be defective. Well, a overclocked 555 is also GREAT for gaming  
£600 = $900,- Budget

CPU: AMD Phenom II X2 555 Black Edition Callisto 3.2GHz - $99.00
GPU: XFX HD-577X-ZNFC Radeon HD 5770 - $159.99
RAM: G.SKILL Ripjaws Series 4GB - $109.99
Mobo: GIGABYTE GA-890GPA-UD3H AM3 - $139.99
HDD: SAMSUNG Spinpoint F3 HD103SJ 1TB - $89.99
PSU: CORSAIR CMPSU-650TX 650W - $89.99
Case: COOLER MASTER HAF 922 - $89.98
ODD: ASUS Black 24X DVD+R - $24.99

Grand total: $800,- (so theres $100 leftover)
There are a few choises of what to do with that $100,-
You could also get a solid state boot drive, a better GPU, a blu-ray burner or a true quad core beast.
Get the Quad Core if you multitask alot.
The Blu-ray if you might use it in the future.
And when gaming, it'll be a hard choise between the SDD and the GPU.