Sepia -> adjust the hue/saturation ... remember to tick colorize
B+W -> either desaturate and adjust levels/curves or use a new adjustment layer->channel mixer and adjust red/green/blue according ... there's some other ways forgot liao
For B&W, always use Channel Mixer. It's more realistic than straight grayscale. I did post a couple of links here on how to do this, you can do a search for it.