I understand that I have to fix bone assignment in MilkShape and test it in the game so many times until I get a good hair animation.

But I want to fix the animation of in the circle part.
In this case Which bone I should use?
I used head, neck and spine_2.
At only these ones is OK?
Or I need to use anything else?

For example spin0, spin1.
What are these bone used for ?

Thank you.

Don't use the neck bone except for hair that actually touches the sides of the neck. For those back areas, do a smooth transition from head to spine2 - no neck assignments.

The bottom part of the hair you might want to use a little bit of spine1.

Spine2, spine1, and spine0 are all bones in the back. Spine2 is between the shoulders, spine1 is midback (around the bra strap level) and spine0 is around the waist, if I recall correctly.

Smooth transitions from one bone to another (like going 70/30, 60/40, 50/50, 40/60, 70/30, etc. as you move from one row to another closer and then further away from a hair joint) will get you the smoothest animation.

You don't have to go in-game to preview your animation, by the way. You can do it in Milkshape. See here: http://www.modthesims2.com/showthread.php?t=270094

Great advice!
Thank you very much, HystericalParoxysm.