You would need to edit the proper frame.html page, depending on which one you are using. We happen to have a space for this at the top of the page which lists the number of items in the cart and the total cost. The code is as follows:
Code:
[ITEMSINCART] item(s) in your cart<br>
Total: [SUBTOTAL]
So the [ITEMSINCART] will give the number of items and the [SUBTOTAL] will give the current sub total.