Awhile back, I decided that it was imperative I have a curtain covering the back half of my desk. No. Actually, I had some purple fabric laying around and was bored. Our desks have a cavernous area, so I figured I'd cover it up so that I could make my desk appear less cluttered and be less distracting for studying.
The string used is all dental floss (braided together at the end). I poked little holes in the cloth in three vertical rows. I threaded the floss through, back and forth, then tied it around a small dowel. I ran the floss across the top of the desk and through a pulley (the yellow thing) of sorts (just to redirect it) and down to the hook (which is actually a part from the floss container) to keep it up.
Some pictures for those of us who can't bother to watch every single video (although it is only 21 seconds):