Remove any old hardware in the window.
Measure your window frame and mark corresponding lengths on the 1-by-3 boards.
Cut the boards along the lines and attach them to form a frame matching the window frame.
Place legs in each corner. Put a small nail in each one to hold it in place.
Screw into the leg through the wood to firmly attach it to the frame. Repeat this step until each leg is attached to two sides with screws.
Screw the window onto the top of the frame and directly into the legs of the table.
Paint or stain the table and the legs.