First Gaming Computer Help

[Midgetboytom]

Hi everybody this is my first post on this forum so sorry that it is asking for help and just shout if anything is wrong with it.

I currently have an old mac and its USELESS so i wanna get a gaming system that i can use for topish end gaming.

i have looked around and come up with this setup:

Case: PCS MAELSTROM T900 BLACK GAMING CASE (£59)
Processor (CPU): AMD ATHLON II X4 640 (2.9GHz/2MB CACHE/AM3)
Motherboard: ASUS® M4A78LT-M LE: mATX MAINBOARD, DDR3, USB 2.0, SATA 3.0Gb/s
Memory (RAM): 4GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 2GB)
Graphics Card: 1GB ATI RADEON™ HD 5770 PCI EXPRESS - DirectX® 11
Memory - 1st Hard Disk: 500GB SERIAL ATA 3-Gb/s HARD DRIVE WITH 8MB CACHE (7,200rpm)
1st DVD/BLU-RAY Drive: 24x DUAL LAYER DVD WRITER ±R/±RW/
Power Supply & Case Cooling: 450W Quiet 80 PLUS Dual Rail PSU + 120mm Case Fan (£25)
Processor Cooling: STANDARD AMD CPU COOLER
Sound Card: ONBOARD 6 CHANNEL (5.1) HIGH DEF AUDIO (AS STANDARD)
Network Facilities: WIRELESS 802.11N 300Mbps PCI CARD (£16)
USB Options: 4 x USB 2.0 PORTS @ BACK PANEL (MIN 2 FRONT PORTS) AS STANDARD
Operating System: Genuine Windows 7 Home Premium 64 Bit - inc DVD & Licence

Price (excluding VAT)
£507.23

Price
£596.00


I have a budget of around £700 but that is for EVERYTHING. including a new mouse/keyboard and an internet security system and all the cables i need.

If you can recommend anything to downgrade/upgrade or just generally change i would be forever grateful.

Thanks
midgetboytom