How to change field value of inserted record in insert trigger for MS SQL

Hello all!

How to change field value of inserted record in insert trigger for MS SQL
6.5... Seems stupid question.....

What I need to do is just translate following example from Oracle to MSSQL
6.5

CREATE OR REPLACE TRIGGER COR.SET_KEY BEFORE INSERT
ON COR.DOCUMENTS
FOR EACH ROW
Begin
   IF :NEW.DOCUMENTKEY is null then
     SELECT core.dockey_gen.NEXTVAL INTO :NEW.DOCUMENTKEY FROM dual;
   end if;
End;
/

Thanks in advance,
Alex