Yeah, a Pentium Dual Core at 3Ghz will never be on par with an i5 3570k, what are you on about? Lol.
Anyways, open the game, go to graphic settings. It should look like this (but different values, also random pic from internet, not mine):

Try setting everything on minimum before:
Video Mode - Drag the slider to the first one (usually 800x600 or so), but keep it at the highest Hz possible (60Hz in a typical monitor, sometimes 75Hz.)
Aspect Ratio - Better leave it at automatic for now.
Reflection Resolution - Set it to Off.
Water Quality - Set it to Low.
Shadow Quality - Set it to Off. This is one of the heaviest options.
Texture Filter Quality - Set it to Low, but this usually doesn't affect the performance that much.
View Distance - Drag the slider to the minimum possible(usually 0 or 1)
Detail Distance - Again, same thing. Drag it to the minimum possible.
Vehicle Density - Just leave it at minimum possible (0 or 1). If you're gonna play IV:MP, having it higher is completely useless.
Shadow Density - This one is very important when you have shadows enabled. It will eat your CPU. Set it to minimum possible (0 or 1).
Definition - Off = Motion blur and slightly blurry view. On = No motion blur, and pixelated view. Leaving it at On usually gives you higher FPS, but may
feel slower. The difference is very small, so it is up to your taste.
Vsync - Since your CPU & GPU are weak, you should just leave it at Off.
After all this is done, play the game and see how it behaves. If you feel it's smooth, you can slowly increase the graphic options.
I recommend increasing the following first before increasing others:
Video Mode. Increasing it will give you a more crisp and less blurry view (and make the chat smaller in IV:MP. But you can change this in IV:MP settings if you don't like it).
Texture Filter Quality. This eats very little FPS in most GPUs.
Reflection Resolution and Shadow Quality at Low. Cars will look better and the world too.
If you still have room, increase Water Quality. You can also try increasing View Distance and Detail Distance very slightly. Probably not more than 15 for both.