Prom help- how is my date supposed to dress? (help soon please- prom is this weekend!)?

It's my senior prom and my boyfriend doesnt have any sort of suit or tux. I found him some black dress pants at a thrift store, but I dont know what type of shirt, tie, vest, or jacket to get him. I know something is suppose to match my dress, but what? The tie? Also, what's the deal with corsages? Does he get them both, or do we each get the other one?