Hi there! I have done window cards, didn't really know there was a technique for it as I learned this about 7 years ago at a stamp camp. The way I was taught was to stamp an image on a square, and then cut the square into fours. When you glue them, make sure you leave a little space in between the squares so it looks like a window frame. Also, glue on to another square card stock cut slightly bigger. Does this make sense? I am doing a Halloween one right now so I will try and take a picture of it. If you want to see it (haven't quite started a gallery yet) you can email me!

HTH!
Joni