Building a gaming pc on a budget

Hi guys, i dont know alot computers but i want to build my own gaming pc. I have a budget of 400-450. i do have some parts which i can use but i help with major things. 

Parts i have 

3gb ram (http://www.computergate.com/products/item.cfm?prodcd=ISRS73FHSC )

Samsung cd drive

500gb solid state harddrive

Amd athlon ii x2 220 (http://www.cpubenchmark.net/cpu.php?cpu=AMD+Athlon+II+X2+220 ) (might not use)

Parts i need help with

power supply, Motherboard, case, video card. ram(if i need to) and cpu.

 

Any help is appreciated.

P.S i do not know alot of specs and stuff so i gonna take your word for it. 

 

Do i need to get extra cooling system.

( http://www.tigerdirect.ca/applications/SearchTools/item-details.asp?EdpNo=4501106&Sku= )

or the 

( http://www.tigerdirect.ca/applications/searchtools/item-details.asp?EdpNo=4501107&csid=_23 ). any ideas?