This sort of photoshopped photography that inserts a historic photo into a present-day image has become pretty mainstream. But if you haven't seen it before, here are some good ones.
WWII Links to the Past :: Sergey Larenkov
This Prague native has put together some images from WWII that give some insight. He did a good job of blending the old images into new that create interesting juxtapositions. At his webpage, choose the names of the photos highlighted in the introductory text to see the images. LINK
A similar set of WWII juxtapositions has been put together by Jo Teeuwisse. She found the historic negatives at a flea market and combined them with her own photography. See them all. LINK
Looking Into the Past flickr Pool
Looking for somewhere to share your own attempts or just want to see more? You can check out the Looking Into the Past flickr pool. And you see that you don't need photoshop to create your own, just a steady hand. LINK