I have used this window technique quite a few times in the past few months. I used it on the last HDR Concert and on HDR Concert#7. It can be pretty tricky to add glass to an image where there once was none. However, all you need is a push in the right direction and you will be making windows in no time!
With a little bit of masking and some help from the Layer Styles panel, windows will start coming alive! In this tutorial I will cover all you need to know by making a port hole in an old rusty boat. Keep in mind you can do this with just about any shape, for the sake of the tutorial I tried to keep it simple