I am trying to follow a tutorial which is specific to Photoshop CS3 but says it can be done in Elements?

Not sure what tools you have in elements but i use the pen tool , draw round the buildings and other stuff you want to keep , make a selection next inverse the selection and now your sky is selected. There are other ways but i would really need to see the pic , it might be easy just to use the magic wand tool to select the sky.