Materials:

• 6 or more yards of fabric (more is better)
• curtain rod and hardware that's not too ugly (if it's in sorry shape, paint it)

Take long, long lengths of cheap fabric -- muslin looks nice and is frequently 99 cents a yard (don't overlook sheets and thrift-shop fabrics too). Wind it around the curtain rods, leaving long lengths hanging at each end. Allow the fabric to puddle on the floor (no hemming necessary) by tucking the fabric edges underneath themselves and puffing the fabric out a little bit.

This is admittedly a decorative look, and not very useful if you want to keep light out of the room. But you could add mini-blinds or shades underneath (which, if you have average size windows, can be inexpensive) or add second-hand sheers.