Shouldn't be any different to storing any other type of data.
Are you having problems testing this normally?
Just create a Stored Procedure to do it, and set the parameter.
Worked for me
HTH
My Example:
*****************
Sql
******************
CREATE PROCEDURE [spname]
@MyNTextParam NTEXT
AS
INSERT INTO MYTABLE VALUES(@MyNTextParam)
*************
c#
*************
SqlCommand cmd = new SqlCommand([spname], [connectionstring]);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.add(new SqlParameter("@MyNTextParam". SqlDbType.NText)).Value
= MyTextArea.Text;
//Open connection and execite cmd