We think we have an abused cat?

In christmas '09 our family got a cat. Vinny was 4 and liked me at the adoption center. We got him home and after a few weeks he only liked my 12 year old sister. We think he was abused. I normal just ignore him, now. He runs next to walls instead of out in the open. Before this I had another cat who dissappeared when he was 15 (peaceful death, we are guessing, so pay attention to Vinny's problem) I know how to handle cats like letting them come to you and putting out your hand. He will pass us in the hall but he is just so frightened and the most timid kitty ever. How can I make him fear us less?