How can I relieve my dog’s anxiety?

I have two miniature pinschers, a boy and a girl, and the boy has some pretty severe anxiety. The female is extremely calm, and only ever barks if the male gets her going. The male min pin seems to get anxious in just about any circumstance outside of his normal routine, for example:
* Barks at the front window when someone passes
* Barks at new furniture, plants, etc. inside or outside the home
* Whines and pants heavily during car rides
* Barks at other …