Usually shampoo will not completely rid cat of fleas (and cats typically do not like baths). I suggest a topical or oral treatment that will rid cat of fleas.
You can use Sergeant's flea shampoo. But in a pinch you can use Dawn liquid dish soap. The Dawn dish soap kills the fleas by clogging up their pores. When you are done with the Dawn you can then shampoo with normal cat shampoo.
Actually the best thing to use to kill fleas on dogs or cats is dawn dish detergeant. Just put the cat in the tub and use a small amount. The fleas will just jump off.