Fw: Oracle/SqlServer/DB2 with unicode

Hi

I am working on an internationalization of a Java application, which can have one of the following as the supporting database depending on the client needs.
Oracle, SQLServer or DB2.
How can I make these underlying DBMS support Unicode ??
I understand for SQL Server specifically, one can use the nchar, nvarchar and ntext types to support Unicode or does It only require database to be installed with 
code set as 'Unicode'?
 
Regards
Rakesh