So I am going to teach you how to make a falling background, honestly they are super easy to make once you get the hang of it. If you have any questions, please just let me know and I can definetly help you out! Program: Photoshop CS3 Extended. I do not promise this works in other programs.
If you only want one pattern moving, ignore the 2 parts and just make 1.
1. Make 2 new images with a transparent background with 300x200 deminsions.
2. Make 2 different patterns in each one using your brushes and such.
3. Once you are done select the image then go to edit>define as pattern with each.
4. Now you can exit out of those images.
5. Now create 2 new images with one demsions as 300x400 and the other as 300x600.
6. Fill the first one with your first pattern and the second one with your second pattern by going to edit>fill.
7. Now create a new image with the deminsions 300x300 and fill with what ever you as the background.
8. Select the love tool in your Photoshop tool bar and move each one of your images and move them to your 300x300 image.
9. Using the selection tool select the entire image then go to the move tool and click ctrl+a.
10. Then you can close the other images besides the 300x300 image.
11. Now open you animation window, window>animation.
12. Create 1 new layer in you animation window.
13. Now select the second layer and move the pattern down so it is in the same posistion as it was before, but just moved down. You might have to switch between each layer to make sure it is in the same spot.
14. Now select both (ctrl and click both the layers in the animation window)
15. Click the tween button in the animation window (the one with the 4 little circles).
16. Frames to add, 30, ok.
17. Delete the last layer in the animation window, it will be number 32.
18. Save by going to file>save for web and devices.
17. Enjoy!
Let me know if this helped you so I can add more helpful tutorials for you!