acer aspire 5536g!!!!!!!!!! need help

[manmathan0431]

hi, i am using acer aspire 5536g notebook my lap specifications
CPU:AMD Turion™ X2 dual-core processor RM-74 (1 MB L2 cache, 2.20 GHz, DDR2 800 MHz)
Chipset:AMD M780G Chipset
Screen:15.6-inch HD 1366×768 pixel resolution, high-brightness (220-nit) Acer CineCrystal TFT LCD
Memory:3GB DDR2
Operating System:Windows 7 ultimate (currently using)
Graphics : ATI Mobility Radeon™ HD 4570 with 512 MB dedicated VRAM
my problem is when ever i play games it lags and lags and lags i cant even play for ten minutes. i play games like fifa 10 and fps games(cod4mw), and i cant play in full screen after i have changed to windows 7 before i used windows vista where i can play in full screen but the games lags in vista and win 7 also. pls help me to solve this problem. my laptop is three months older. pls help me?????????