With the tax credit this year, I want to put in some replacemant window inserts. What do I need to know? I have six general double hung windows. What do I have to remove? These have aluminum guides and springs on each side of the sash to hold the window up. I hear the measuresments are critical--from where to where? I know that I have to remove the stops. How about the trim--looks like that could stay. I have questions about the stool and the sill. ????? I have aluminum storm windows on the outside...apparently storm windows are a thing of the past. Thanks for advice in advance.