Ta-Da! Here is the cheerful outcome of my window project. I learned as I went along, making some mistakes along the way, but for the most part, I am HAPPY with how they turned out.
Remember these crusty old windows and my post about giving them new life?
Step 1: Scraping off and cleaning up. I first gave the windows a vigorous brushing with my broom. Then I used my spatula to remove excess paint. I left as much paint on as possible, only scraping off that which was literally already falling off. I did not use a sander because I knew it would take everything off!
After using my broom and spatula, I thoroughly cleaned both sides of the glass with a window cleaner.
Step 2: Choosing and cutting your paper. I chose many pieces of high quality scrapbook paper (it's thick) that were different patterns and colors, and yet would coordinate with each other and the colors in my house. I placed them all on a table and began playing with how they looked together - changing their places, taking some away, etc. 
After playing around with different combinations, favorite patterns begin to emerge.
Cut your papers the size of your window panes and get ready to paint on your goo.
Step 3: Mod Podge Mania. First let me say I tried my Diamond Glaze which is extremely clear and I use for small projects... and I nearly ruined a piece of paper. Keep the Diamond Glaze for small projects! Good 'ol Mod Podge is the BOMB. Brush a generous, even amount on the decorative side of your paper - because it needs to soak in a bit (remember, the paper is thick) - and then carefully place it on the glass pane.
Working from the middle to the edges, use your FINGERS to smooth out air bubbles. I know the pic shows me using a credit card, but this ended up spreading too much Mod Podge around. Your fingers will be enough to smooth out air bubbles - you can even hear the little "snap" the bubbles make.
No worries! When you turn your window over it may look like this at first! The Mod Podge will dry clear and the cloudiness will go away, so stop having a heart attack - it will look just fine :) 
YIPPEE!!!
~ Other Ideas ~
The possibilities are endless! Here are just a few!
*put 2 windows vertically to make a headboard
*print out black & white versions of family or vacation photos to put in panes
*put monograms, initials, or even words on the pieces of paper before Mod Podging
*use favorite fabric remnants instead of paper
... and if you're wondering what I'm going to do with the third window... well, it's going to be a mosaic! That's my summer project - my first attempt at a mosaic, and something I've always wanted to try.
