Baskar,
Copying the namespace is not possible. Although creating the namespace with same name is possible but not recommended. It may lead to naming conflict in object names as the system as system also warns.
Having said that, if you copy objects, it has an option (With all dependant objects). You can use this option and you won't have to copy for example, message type/data types etc if you copy a service interface.
Hope it helps!
Ambrish