HEEELP GTA IV

Hello,i have a problem like that too.. my pc is
quad core...
specs: System
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Manufacturer Gigabyte Technology Co., Ltd.
Model GA-MA785GMT-UD2H
Total amount of system memory 2,00 GB RAM
System type 64-bit operating system
Number of processor cores 4

Storage
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Total size of hard disk(s) 235 GB
Disk partition (C:) 132 GB Free (233 GB Total)
Media drive (D:) CD/DVD
Disk partition (F:) 25 MB Free (2 GB Total)

Graphics
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Display adapter type ATI Radeon HD 4200
Total available graphics memory 1022 MB
Dedicated graphics memory 512 MB
Dedicated system memory 0 MB
Shared system memory 510 MB
Display adapter driver version 8.641.0.0
Primary monitor resolution 1920x1080
DirectX version DirectX 10

i run it on the lowest graphics possile but still it lags like hell and i have windows 7 it automatically installs all the updates like .net framework... HELP GODDAMNIT! it's imba for me!