Replacing double hung wood windows with vinyl ones is about the simplest and most cost effective of all window replacements. That is as long as the main frame of the existing window is in good condition and can be reused. Here's how it happens. First, all of the trim is removed from the four inside faces of the main frame. No, you don't have to remove the ropes and weights. They can be left in the hollow sides of the window frame. However, we do suggest spraying expansive foam into the balance of the void to improve energy efficiency. After the trim is removed it becomes apparent that the main frame has and offset in it that goes all the way around. The inside half of the frame is slightly smaller than the outside half of the frame. The replacement window comes in its own frame and is set in place from the outside fitting into the larger opening and butting up against the face of the smaller portion of the frame. Editor's Note: If the main frame doesn't have a jog wood trim is added to create one. Trim is used to cover the caulked joint between the frame of the new window and the old one. Our first double hung window replacement job took about 60 minutes per opening -- soup to nuts -- removal, installation, caulking, trim and paint touch-up. This is definitely a DIYer project.