Okay, I will try and make some more detailed instructions over the next few days with photos... and I'll edit these for clarity later. I guess it's probably about a 6 or 7 out of 10 on a difficulty scale? Didn't take me longer than an hour though!
but basically here is all I did..
1. choose a card size ( I did 5x7) I had existing cards and just glue sticked everything onto them.
2. to print you'll need 1 5x7 of the front colour, 1 5x7 of the inside colour, and all the elements you want. A kit that has lots of pieces, flowers, animals, etc. that are easily cut out works best.
3. paste (gluestick/mod podge, etc.) your backgrounds to the very front and the inside of the card.
4. Cut your window. I used a bowl, and basically laid it on the card and drew and arc over it with a craft knife. The edges looked bad when I was done, but I just sanded that away with a little nail file in like 10 seconds. no biggie! All better.

Cut an arch so that the base is about 1.5 inches from the bottom open end of the card.
5. Cut a slit in the back of the card - the same distance up as the bottom of the arch on the front of the card. The slit should be about 5 inches long.
6. Now the front arch should fold down inside the card, and stick through the slit at the back, so that the whole card stands on it's own, with a little stage. Now, you can use foam dot stickers or glue dots, etc. to affix your pieces. If you are doing flowers, place some on the front of the card, and some just inside the window you've created. To place some on the 'stage', make small "L" shaped peices of cardstock, and glue one side to the piece, and one side to the card so that the element can fold up and down. Place pieces at different locations on the stage to give the card lots of dimention. When the card is folded flat, with the arch flap up in its original position, all of your elements should fold flat as well.
I hope this makes sense???