Looking for a little advice regarding a mid to low end gaming desktop

[RogueShenanigans]

As the title reads, I am looking for some suggested specification on a decent gaming desktop. I am more of a strategy gamer than an action gamer so my expectations are fairly limited. The most demanding game I suppose I would be looking to run would be Arma II at a reasonable level if at all possible. By budget is £500 to ~£650 and I would like room to expand the machine as I come into more money. I have a copy of Windows 7 64 bit so that should not be included in the spec, which should give you gents more room to play with.

I won't insult you by trying to post example specs as I would look like a fool at best and cause misunderstandings at worst.

Thanks in advance.

[Fear]

If you could push your budget to £661 i would go with this spec below but up the PSU to a 650W corsair as they are a branded and much more reliable PSU also you will not be as restricted in a year or 2 if you want to upgrade to a higher performing GPU and add any extra HDD's etc.

CasePCS MAELSTROM T900 BLACK GAMING CASE
Processor (CPU)AMD BULLDOZER QUAD CORE FX-4100 (3.60GHz/4MB CACHE/AM3+)
MotherboardASUS® M5A97: AM3+ PLATFORM, DUAL DDR3, SATA 6.0GB/s, USB 3.0
Memory (RAM)8GB SAMSUNG DUAL-DDR3 1333MHz (2 X 4GB)
Graphics Card2GB AMD RADEON™ HD7850 - DVI,HDMI,2 mDP - DX® 11, Eyefinity 4 Capable
Free ItemFREE DIRT SHOWDOWN GAME with any AMD 7000 Series GPU!
Memory - 1^st Hard Disk500GB WD CAVIAR BLACK WD5002AALX, SATA 6 Gb/s, 32MB CACHE (7200rpm)
1^st DVD/BLU-RAY Drive24x DUAL LAYER DVD WRITER ±R/±RW/RAM
Power Supply450W Quiet 80 PLUS Dual Rail PSU + 120mm Case Fan (£29)
Processor CoolingSUPER QUIET 22dBA TRIPLE COPPER HEATPIPE AMD CPU COOLER (£19)
Sound CardONBOARD 8 CHANNEL (7.1) HIGH DEF AUDIO (AS STANDARD)
Network Facilities10/100/1000 GIGABIT LAN PORT - AS STANDARD ON ALL PCs
USB Options6 x USB 2.0 PORTS @ BACK PANEL (MIN 2 FRONT PORTS) AS STANDARD
Operating SystemNO OPERATING SYSTEM REQUIRED
Office SoftwareNO OFFICE SOFTWARE
Anti-VirusNO ANTI-VIRUS SOFTWARE
Warranty3 Year Silver Warranty (1 Year Collect & Return, 1 Year Parts, 3 Year Labour) (£5)
DeliverySTANDARD INSURED DELIVERY TO UK MAINLAND (MON-FRI)
Build TimeStandard Build - Approximately 10 to 12 working days
Quantity
1

Price: £621.00 including VAT and delivery.

[RogueShenanigans]

Thanks for your input Fear. If I decide to go with that build I can stretch my budget to acquire that higher end power supply as I favour flexibility going forward.