What can I do about this dog?

I live in a very quiet neighborhood, the houses are not that close from eachother. I live in a duplex and a young single guy just moved in about a month ago. He has a small dog (terrier mix) He used to have her inside and she'll come out and play w my dog several times during the day. He left for the weekend and she pooped inside the house, ever sinse he has tied up in the backyard. My problem is that he does not feed her at all or give her water. She is closer to my window than to his apt. And I hear her barking constantly. It does not bother me her barks, but it kills my concience knowing that she is hungry. I often go out and feed her, but my husband is getting annoyed w that. It's hard enough to afford food for our dog. My husband won't say anything to the guy. And I don't want to deal with him either. He seems really nice though. But the dog needs help. I am tempted to let her loose. I don't have a car can't take her to a shelter. What can I do to help her? Without causing problems w my neighbor?