i want build cheapest gaming pc for my little brother!

NBSN

Admirable
That link does not work correctly. And no you cannot because the operating system if going to be $100 or so, unless you go with a free one like Linux or already have an unused copy of Windows lying around.
 

NBSN

Admirable
I personally think that system is horrible and will not run the game at decent settings and fps...but to each their own.

I offer up this system:

PCPartPicker part list: http://pcpartpicker.com/p/2KvCFT
Price breakdown by merchant: http://pcpartpicker.com/p/2KvCFT/by_merchant/

CPU: AMD A10-6800K 4.1GHz Quad-Core Processor ($119.96 @ OutletPC)
Motherboard: Gigabyte GA-F2A55M-S1 Micro ATX FM2+ Motherboard ($36.98 @ Newegg)
Memory: Team Vulcan 8GB (2 x 4GB) DDR3-1600 Memory ($65.99 @ Newegg)
Storage: Hitachi Ultrastar 1TB 3.5" 7200RPM Internal Hard Drive ($48.00 @ Amazon)
Case: Diablotek DIAMOND ATX Mid Tower Case w/400W Power Supply ($29.99 @ Micro Center)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($84.99 @ NCIX US)
Total: $385.91
Prices include shipping, taxes, and discounts when available

Which is many times more powerful than the used Dell one, and the price includes the operating system.