Hi,
not sure about this, as we haven't 4.0 systems any more. But, like Mike042, I think it should be in file /etc/routes.
Two ideas:
Have you read the manual?
man routes might help.
Create a file /etc/routes with contents as described above, and permissions 644.
You may have to restart your net services (or at least use a kill -HUP) in order to make the change effective.
hope this helps