Hi,
due to a general policy, we tend not to give a complete solution to what seems like homework. Instead we ask you to try to do something and write some code. Then we can discuss it and fix the errors.
Besides, you should try to be a little more specific about your problem. Do you want to build an implementation of a Binary Search Tree which allows inorder and postorder traversal? Or do you want to construct a Binary Search Tree by knowing its inorder and postorder representation? It seems to me the second is more likely...
Ok. Are you sure it is in-order and not pre-order? I'm asking this because an in-order traversal of a Binary Search Tree will always give the sorted list of its elements. Thus I don't know what interesting information we could get from this...