Thank you for helping. I'm using these in a game engine. Following the last section you pasted in above will not work. The problem is that in the Run sprite sheet (specifically Unicorn_Run.png), there more transparent area on the right and left edges of the sprite sheet than 1/2 the area between images. The left and right have to be 1/2 the spacing that is between the images. Also, I'm not certain if all the images are spaced equally or not but they need to be. In the game engine, you can only tell it the width of the image and how many images are in the sheet. It starts at the left and cuts it into an equal number of images as it goes to the right.
Thanks,
Brian