i think there's different forms of the vitamin b3 (niaciamide being one of them).
it has /not/ been known to help acne when taken orally. you need to apply it topically w/ a base (aloe gel works well). just get some pills and grind them up (coffee grinder...or just smash them with something until they're in a powder form....or you may be able to find a powder form of the pill)
then every night before you go to bed mix it in w/ some aloe vera, and apply it to the affected area.