The piece you are trying to turn is most likely reverse threaded. On cheap one piece cranks you should be able to get away with using a 16mm open end wrench on the flats...its not ideal but will do in a pinch. If the fixed cup is truly seized then you will either need to spend the $15-$20 on the proper tool (Park makes one) or have a bike shop do it for you. Try turning in the other direction first though.

-j