ASTM / HL7 communication via Ethernet shield

I have a device which claims to communicate via TCP/IP in either client or server mode.
It should communicate using ASTM or HL7 communication protocol.

I have a simple question.
Is there an easy way to set up the Arduino with Ethernet shield to act like a server, and responds to requests with an ?
I want the the Arduino to listen on a specific port, and when it receives a byte(05) - or , I want it to respond with byte(06) or - and monitor all communication in between…

Not sure if anyone has a library or site which explains how to do this? Or even if it is possible??
And will I need a network hub or switch to accomplish this task or can I connect the device directly to the ethernet shield using a CAT5 cable??

Any insight would be greatly appreciated.

Thanks
Scott

Ok - lack of response is a bit discouraging... Perhaps I should try bite size pieces:

Forget the HL7 part of the question... let's start with this one. 1. Can I establish a CAT5 cable connection to a computer directly using the Ethernet shield or do I need a hub?

So I would have

Computer's Ethernet port---- cat5 cable -------EthernetShield ||||||||||||||||||||||| Arduino ----------USBcable-----------Laptop

You can connect the ethernet shield directly to a computer with a CAT5 cable, but you must use static ip assignments on both the Arduino and the computer unless you can set up the computer's ethernet port with a dhcp server.