Measure the width and height of the bookcase. Jot down the measurements to take shopping with you.
Select a tension curtain rod that will fit in the width of your bookcase. Select two curtain panels that are long enough to cover the entire length of the bookshelf. If you can't find an exact match, purchase curtains slightly longer.
Hem the curtains, if necessary, to match the length of the bookcase.
Adjust the tension rod to fit snugly into the built-in bookcase. Remove the rod, slide it into the curtain pocket or rings, and put it back at the top of the bookcase.
Measure the width and length of the bookcase and take down the measurements.
Purchase a curtain rod that will accommodate the width of the bookcase. Make sure your rod comes with mounting hardware. Purchase a curtain that will accommodate the length of your bookcase.
Hold the mounting hardware to the top upper corners of the bookcase. Make marks where the screws will go. Drill pilot holes where you made the pencil mark. Put up the mounting hardware and screw it in.
Adjust the rod length to straddle the mounting hardware. Put the curtains on the rod and place the rod on the hardware. Hem the curtains, if necessary.
Measure the width and length of your bookcase. Purchase a curtain or a piece of fabric large enough to accommodate it.
Hem your fabric, if necessary. Cut a strip of Velcro the width of the curtain. Remove one side of the strip and sew it across the top edge of the curtain.
Hot glue the other side of the strip of Velcro to the front top edge of the bookcase. Affix the curtain to the bookcase by lining up the strips of Velcro and pressing them together.