How to install an air conditioner in a storm window?
AC unit has a bracket, but as it is a storm window, I'm not sure about how to install the bracket on the metal storm window. Also, the bottom of the window is not flat, as there is a lip which is 1 1/2 inches above the inner sill.
Try building a frame for the AC unit to sit in using 2x4's. Use a chisel or saw to shape the outside of your new frame to fit snugly in the window, then put the AC unit into that. If it is on a ground floor window, you may want to brace the outside of the unit with another 2x4 running from the AC to the ground.