you definitely need to have your bodyshop deal with the other company. I would say in no circumstances should you cash that check. That can be seen as you agreeing to the amount as a final payment in court.
Also, you need to go after diminished value. Thats the loss in value because your car has been in an accident. Best way to get an amount for that is to talk to the used car manager at your selling dealer and ask how much less its worth after repair than if it had never been wrecked, and then pursue that amount with the insurance company also. I'm not sure about California, but in Georgia, they are required to pay it.
http://askville.amazon.com/entitled-...uestId=2662314