Check out the build up above. In the first PCpartpicker link. It can be changed up, certainly improved, if you want to spend a little more.
Planet Side/Planet Side 2 is very nivida optimised game when it comes down to the video card this is a little over £600 with windows+a full 1080p monitor
http://uk.pcpartpicker.com/p/1bBgz
CPU: AMD Phenom II X4 965 Black 3.4GHz Quad-Core Processor (£63.59 @ Aria PC)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£24.49 @ CCL Computers)
Motherboard: Gigabyte GA-78LMT-USB3 Micro ATX AM3+ Motherboard (£38.54 @ CCL Computers)
Memory: G.Skill Ares Series 8GB (2 x 4GB) DDR3-1333 Memory (£39.99 @ Amazon UK)
Storage: Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive (£39.00 @ Amazon UK)
Video Card: EVGA GeForce GTX 660 2GB Video Card (£149.98 @ Amazon UK)
Case: NZXT Source 210 Elite (Black) ATX Mid Tower Case (£41.99 @ Amazon UK)
Power Supply: Corsair CX 500W 80 PLUS Bronze Certified ATX12V Power Supply (£49.83 @ Dabs)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer (£13.15 @ Amazon UK)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) (£68.35 @ CCL Computers)
Monitor: Hannspree HE225DPB 21.5" Monitor (£89.83 @ CCL Computers)
Total: £618.74