Gets hang while playing the game

Hello,


hi... my system configuration
intel pentium dual cpu e2180 @2.00 GHZ
Mercury PI945GCM - Mother board
1 GB ram
160 Hard Disk
Today i bought Radeon HD 4650 Graphics card ...@ cost 2800 /-

i am able to play nfs hot pursuit 2010 and Assassin's creed 2
but the problem is "IT GETS STUCK STUCK WHILE PLAYING GAME".

Though i have 1 GB Graphics Card still its Stucking...i have lost interest in playing games on my pc..

please help me...!!! :(

should i upgrade my RAM bcoz Mercury Pi945GCM is saying that it should have MINIMUM 1 GB RAM ..so i ve a doubt on dat ...pls help me . i am bworried a lot...