Unicode in Oracle9i

Hi all,

I'm learning Oracle9i, I connect to Oracle Server by isqlplus (Web Browser is IE 6.x). I like to add a row with unicode data into a table. Please review my below code:

Create Table Employees(EmpID char(10) primary key, EmpName nvarchar2(50));

Insert Into Employees Values('Emp01', 'Nguyễn Văn Tuấn');
or
Insert Into Employees Values('Emp01', n'Nguyễn Văn Tuấn');
or
Insert Into Employees Values('Emp01', N'Nguyễn Văn Tuấn');

But I can't get a expected result because of the unicode string automatically translates to 'Nguy?n V?n Tu?n'

Anybody knows how to correct this error?
I look forward to hearing from you.

Thanks in advance,
TrauVang