Oracle Database Express Edition (XE)

Any help would be great, I'm not sure what I'm doing wrong.

I was trying to run a simple PL/SQL procedure just to test outputting information to the screen

SET serveroutput on;
BEGIN
dbms_output.enable;
dbms_output.put_line('Procedure Test');
END;
/

and this error came up "ORA-00922: missing or invalid option"

When I looked in object browser to see if the dbms_output package was there it wasn't listed. Am I missing something? Isn't that one of the Oracle supplied packages when you install Oracle XE? In fact there was only one package listed DBMS_REPCAT_AUTH, did I miss downloading something?

Please Help!!!