I am doing something wrong it seems:
the game recommend me to play on high if I do that everything looks great when stand still no fps problems but when I move its choppy as if I am skipping some frames. This is the same when I tweak the options to lower settings, res and all the other things included.

Please tell me what I am doing wrong!
My system is : Phenom II X4 965(3.4GHz) 4GB DDR3 AMD Radeon HD 6670 Windows 7

The 6670's not likely to keep up with the game except at reduced resolution and settings. It's below minimum requirement, but you should be able to make the game playable.

Choppiness is usually due to interfering crapware or excessive expectations. Junk like indexing programs and updaters for installed programs is obvious; things like antivirus with real-time file protection can sometimes be the offender; arguments between USB devices can make the game unresponsive to the mouse.

But this game is not an FPS and does not run like one. It does not compromise rendering to maintain frame rate. Some frame dropping is going to happen, even on powerful rigs.

I don't think its the video card. I checked with fraps the low and high settings are almost equal in fps (7-20)