Hi Derek,
There are some options you have to do this. You can use the TCP/IP, Datasocket, or VISA libraries to perform your communication. Depending on what you are trying to do and what kind of instrument you are working with, you may look into using the VISA library, and then instead of passing a GPIB address you pass a socket resource. Here's a link to more information:
Link.
For information about raw ethernet packets, check out this thread:
ThreadJeremy L.
National Instruments
Jeremy L.
National Instruments