Hi
If you configure the Ethernet controller and send data using its buffer descriptors you don't need to use any OS.
You can take existing initialisation code (also from projects using OS) as base since it has nothing to do with the OS itself.
Depending on what type of data you want to send you may need to develop a number of protocols to go on top of it though, which may take a month or two of work to achieve some basic operations to be compatible in a network. For a reasonable level of Internet protocol compatibility you may need to plan for 6 months to a year or two. During the work you may however decide to use an OS to simplify the management of the tasks and achieve reliability.
If you need just fairly simple TCP/IP you can take something like OpenTCP which doesn't include any OS or file system support: http://sourceforge.net/projects/opentcp/
You can also take LwIP without MQX and add your own scheduling and file system (if needed).
Regards
Mark