arm and hammer has this stuff.
One is an Arm and Hammer Allergen Reducer. I had originally seen and used it as a powder, but when i went to buy it again, it was only available in a spray.
You spray it on your carpet, let it dry for 5 min, then vacuum it up. There is something in it that releases the static charge that normaly keeps your cat hair stuck to the carpet.
They also have, in powder form, Arm and Hammer Pet Odor Remover? (i can't remember the name exactly) But it does the same thing, it just doesn't have any anti-allergen properties evidently. It releases the static charge from the carpet and allows you to vacuum it up.
I would also suggest if you vacuum combs the hair one way, you could vacuum your room twice. Once once long ways, to get the hair going one way, and then once width-ways to vacuum the hair perpendicular to the way the first vacuuming had layed it out. It would be easier for the brush to grab that way.