Im thinking of buying a a gigabyte MB with B75 chipset and an Ivy Bridge i5 3450 (its HD2500 IGP).I already have a sapphire radeon hd 6570 (2gb ddr3). Im using a 4:3 17" monitor so i dont need a better graphics card for gaming. So my question is will the Ivy bridge hd2500 help me in any way with gaming performance?
No you cant use both of them together. Nvidia and ATI both have solutions for joining graphics cards together.
However, Intel has built the integrated graphics chipset in your motherboard so it will be incompatible with your ATI card.
You are limited to using one or the other. Which one is more powerful I could not say.