First PC Build (Gaming - £700)

[AurohnVersus]

I'm a complete newbie when it comes to building PC's, the only experience upgrading I have is RAM. How difficult will it be? What if I break something? If I build it and a part doesn't work what do I do? Would it be worth paying extra to get someone to put it together for me? Any other advice?

As in the title, I'm looking for a Gaming build for around £700, I'm looking to play current and future games (2012-) at medium settings at least.
I have a general idea of the parts I want and I don't need any Accessories or OS.

I've been looking at these parts to get so far:

Asus P8P67 Pro R3 Motherboard
http://www.ebuyer.com/260185-asus-p8p67-pro-r3-p67-socket-1155-8-channel-hd-audio-atx-p8p67-pro-r3]
Intel Core i7 2600k 3.4GHz
http://www.ebuyer.com/252535-intel-core-i7-2600k-3-4ghz-socket-1155-8mb-cache-retail-boxed-processor-bx80623i72600k]
XFX Radeon HD6870 1GB
http://www.ebuyer.com/247429-xfx-hd-6870-black-edition-1gb-ddr5-dual-dvi-hdmi-displayport-pci-e-hd-687a-znbc]
Kingston 8GB DDR3
http://www.ebuyer.com/248449-kingston-8gb-2x4gb-ddr3-1333mhz-hyperx-blu-memory-kit-cl9-1-5v-khx1333c9d3b1k2-8g]
Samsung 1TB SATAII Hard Drive
http://www.ebuyer.com/173804-samsung-hd103sj-spinpoint-f3-1tb-hard-drive-sataii-7200rpm-32mb-cache-hd103sj]
Samsung 22X DVD RW Optical Drive
http://www.ebuyer.com/268621-samsung-sh-s222ab-22x-dvd-rw-dl-ram-sata-optical-drive-oem-sh-s222ab-bebe]

Suggestions for the additional parts? Anything I should change? Preferably from ebuyer but others based in the UK is fine.

 

[Why_Me]

This build allows you to add another one of those cards later on for SLI.

http://www.ebuyer.com/221737-coolermaster-cm-690-ii-lite-version-rc-692-kkn3 £56.99 inc. vat
Coolermaster CM 690 II LITE

http://www.aria.co.uk/Products/Components/Power+Supplies/700-950W/750W+XFX+Core+Edition+80PLUS+Bronze+Power+Supply+?productId=45334 £71.92 inc. VAT
750W XFX Core Edition 80PLUS Bronze Power Supply

http://www.dabs.com/products/gigabyte-z68a-d3h-b3-lga1155-intel-z68-ddr3-atx-7HYP.html £99.99 inc vat
Gigabyte Z68A-D3H-B3 LGA1155 Intel Z68 DDR3 ATX

http://www.novatech.co.uk/novatech/prods/components/processors/intelcorei3,i5andi71155socket/intel/bx80623i52500k.html £159.98 inc vat
Intel Core i5 2500K 3.3GHz Socket 1155 6MB Cache Retail Boxed Processor

http://www.aria.co.uk/Products/Components/Fans%2C+Heatsinks%2C+Coolers/CPU+Coolers/Coolermaster+Hyper+212+Plus+CPU+Cooler+?productId=39577 £21.88 inc. VAT
Coolermaster Hyper 212 Plus CPU Cooler

http://www.ebuyer.com/264750-g-skill-8gb-2x4gb-ddr3-1600mhz-ripjawsx-memory-kit-cl9-9-9-9-24-1-5v-f3-12800cl9d-8gbxl £44.99 inc. vat
G-Skill 8GB (2x4GB) DDR3 1600Mhz RipjawsX Memory Kit CL9 (9-9-9-24) 1.5V

http://www.novatech.co.uk/novatech/prods/components/harddrives-internal/sata500gbto1tb/samsung/hd103sj.html £40.98 inc vat
Samsung Spin Point F3 SATAII 1TB 32MB Cache Hard Drive <8.9ms 7200rpm - OEM

http://www.ebuyer.com/220986-sony-optiarc-ad-5260s-24x-dvd-rw-dl-sata-optical-drive-oem-ad-5260s-0b £14.99 inc. vat
Sony Optiarc AD-5260S 24x DVD±RW & DL SATA Optical Drive - OEM Black

http://www.novatech.co.uk/novatech/prods/components/nvidiageforcegraphicscards/nvidiagtx560tifermiseries/msi/n560gtx-tf2.html £169.99 inc vat
MSI GeForce GTX 560TI Twin FrozR II 1024MB GDDR5 PCIe

Total: £617.71 inc vat

http://www.novatech.co.uk/novatech/prods/components/motherboards/intel1155p67chipsetmotherboards/asrock/90-mxgfs0-a0uayz.html £124.99 inc vat
ASRock P67 Extreme4 Intel P67 (Socket 1155) Motherboard - B3 Revision

http://www.novatech.co.uk/novatech/prods/components/cases/cases/coolermaster/sgc-2000-kkn1-gp.html £56.98 inc vat
Coolermaster Storm Scout Gaming Case - Black (No PSU)