Ah, my bad.
I think he just wants to know how to comp them in Photoshop.
We have a tutorial on that topic called render layers in production, it's by Izzy who works in broadcast and it's really good for getting an insight into post work. It was done in Maya 8.5 so a few buttons have been moved but I followed it just fine in 2011, it also uses After Effects but it demonstrates the principle so any post app works.
I'd love to see a tutorial covering all the normal render passes for example ambient (even though there is already one) , beauty, reflections, shadows and dof (particularly this one) .