rama.stefan the DuinOS files would need to modified to accept the Mega 2560. There isn't much of a difference between them.
Bima yes, the Ethernet library works "as is" provided no other SPI devices are being used. The Ethernet library needs to be initialized within the task declaration using the portENTER_CRITICAL() call as shown in my posted example (e.g. vNetSvcTask). Also, this was tested and is being used on a mega and not the Uno (limited RAM).
Eric