The first thing that you want to do is in a new image, create a new transparent layer. Then you want to use the oval shape tool and check "fixed" so that it forms a perfect circle. Draw the circle, fill it with any color that you want, and then duplicate the layer. Use the move tool to move the new circle underneath the one you just created, leaving some room. Merge this layer with the one you originally copied it from, and repeat this step until you have as many circles as you want. Then you want to go to the script-fu menu and apply an inner bevel with 16 softness. Repeat the previous step, only use outer bevel instead. Repeat the previous step, only set the direction down. Next click the "eye" next to the background layer to hide it, select your dots layer and merge visible. Finally, make the background visible again, then create a drop shadow with 100% opacity, with no offsets and a blur radius of 3 and you are done.