What do you with greasy hair and dandruff?

My hair gets really greasy at the top of my head, but at the same time my scalp is dry and I have dandruff. My hair is wavy-curly, so when I try to brush it to spread the grease from the patch of my head my hear gets really frizzy. When I shampoo my hair really well, my hair is no longer greasy when it dries, but my the ends of my hair are frizzy and dry, and I lose my natural curls. How can I fix this mess?