The function you're looking for is called "Smart object", available from PS CS2
You can basically create a master picture that has secondary pictures connected to it. By double clicking on the proper layer, you open a secondary picture, can modify it etc. and see the modification on your master picture.
As long as there are no overlaps of the pictures, it's great. Otherwise, since layers are modifying each other through the transparency and all the various effects, this function is helpless.
Have a look there to become more familiar with this function
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