Gta 4 is running lagging


i am facing fps problem in gta 4.

my system is windows 7 ultimate SP 1
intel core 2 duo CPU E4500 @2.2ghz 2.19ghz
RAM 2gb
intel G41 express chipset

i am getting average 8 fps. is there anyway to get 30-40 fps or at least 30 fps.
and i had 64 mb dedicated video memory but some time ago i made changes in bios and made it 128 mb