The idea behind my project is to make some Arduino boards communicate viaIPv6 through XBee and Ethernet.
After a day of study of Contiki I learned that to realize the idea I needto implement a radio driver for XBee and here comes the first questions:- is it right?
Communicate with what? The XBee and Ethernet shields serve vastly different purposes.
The Ethernet library does not currently support IPv6.
What is Contiki? I don't think you need to "implement a radio driver".