Cat Advice, anyone?

I live with a crazy cat. Seriously. He ends up tearing through the apartment at warp speed. I think sometimes it's when he's mad at us, but mostly it seems pretty darn random. He stalks us when we walk through the apartment. Not from the front, no! He comes up and bites us from behind. It's crazy. He knows we'll be able to see him if he comes at us from the front.

He has his moments when he cuddles up with us, sure. But those times are few and far between. He'd rather gnaw on our hands or feet!

We've been thinking about getting another cat on the premise that the current cat doesn't really know how to be a cat. He was only 3 weeks old when we adopted him. His behavior isn't getting any better, and I'm afraid that he's always going to be wild if we don't do something now. Anyone have any hints, tricks, tips, advice?