Gaming/Internet PC build for £600

Hey, I'm building a PC. I have been looking into making one and I have tried to think up my own build, but (having no experience before) been unsuccesful. So, I'm asking for any recommendations for parts.

Approximate purchase date: Within this month/next month. Budget range: £600
System usage from most to least important: Hard internet use, gaming.

Parts not required: OS.

Preferred website for parts: Any that ship to the UK
COUNTRY OF ORIGIN: UK, England

Parts and preferences:

Overclocking:

SLI or CROSSFIRE:

MONITOR RESOLUTION: 1440x900

ADDITIONAL COMMENTS: Again, this is my first ever build, I have no previous desktop to work from, as the only PC that is in my possession is my crappy ACER laptop and I have no idea what parts are reccomended.

Here is a PC I put together...

Cost: £517.31 ex VAT (£594.91 with VAT)
CPU: AMD Phenom II X3 Tri Core 720 Black Edition 2.80GHz (Socket AM3) - Retail
MOBO: Asus M4A785TD-M Evo AMD 785G (Socket AM3) PCI-Express DDR3 Motherboard
HSF: Coolermaster Hyper 212 Plus (Socket AM2/AM2+/AM3/775/1156/1366)
RAM: Patriot Sector 5 Viper II 4GB (2x2GB) PC3-10666 1333MHz Dual Channel (PVV34G1333LLK)
HDD: Samsung SpinPoint F3 500GB SATA-II 16MB Cache - OEM (HD502HJ)
GPU: HIS ATI Radeon HD 5770 1024MB GDDR5 PCI-Express Graphics Card
PSU: Corsair TX 650W ATX SLi Compliant Power Supply (CMPSU-650TXUK) More than you need now but a great PSU to build on
DVD: Samsung SH-S223B/RSMN 22x DVD±RW SATA Dual Layer ReWriter (Black/Silver/Biege) - Retail
CASE: Coolermaster CM-690 Dominator Case - Black (No PSU)