Reving a MMO Game: Decompress PCAP File

So we are trying to recreate a old dead MMO game but we dont know how the Old MMO sent the data to the client.​ Must have knowledge in how a to use a packet sniffer and knows how to decrypt packet logs. I need to know how the packet is structured. IE the fields and their order, Just overall structure of the packet, Opcode, and Header unpacked data order. This packet has important character data in it. Their is no encryption, It is compressed with the zlib library. Must finish fast (2 days)