Rubber Glove Method
Put on a pair of clean rubber gloves. Dampen the gloves under water from a faucet, as suggested by Cats of Australia.
Run your dampened, gloved hands down the length of the curtain. You'll notice the fur clings to the gloves.
Rinse the accumulated cat hair off the gloves and repeat until the curtains are hair-free.
Pet Hair Roller (or Duct Tape) Method
Use a pet hair roller on the brush. These rollers have sticky, disposable tape on them that you simply roll over the curtain.
Tear off the first layer of tape when it is full of hair. Beneath it will be a fresh sticky layer.
Alternatively, you can use duct tape (or double-sided tape) to do this. Wind the tape around your hand, sticky side up, and pat at the curtain.
Repeat rolling or patting the curtain until the hair is gone.
Sponge Mop Method
Wet a clean sponge mop in clean water. You can just use a sponge if you do not have a sponge mop. Wring it out well so it is only damp and not dripping wet.
Wipe the curtains, starting at the top and brushing downward with the sponge. Cat fur should cling to the sponge.
Rinse out the mop head in warm water to remove the collected hair. Wring it out again and wipe it again over the curtain--continue until all the fur is gone.