Cheap computer Set Up

Thanks for looking firstly,
Secondly, I need a fairly resonably priced computer to run games, and demanding ones too, such as COD 7 and i have done a bit of research and found that this is probably the most likely set-up to buy. Im 16 so i dont understand these things too much but any help or suggestions would be appriciated




The computer itself :
http://www.iibuy.com.au/index.php?main_page=product_fre...

The min specs for CoD 7 :
http://www.game-debate.com/games/index.php?g_id=703&game=Call%20of%20Duty%207


My main question is, would this computer do the job (considering i will buy another graphics card later ) and will it do it well? and im asking this because i have read on other forums that building your own computer is cheaper, i just find this a very convinient set up. Thanks.