I have a 3 month old male ferret, Kuba, who likes to harrass my cat, Katina
too.  Katina would run to me for help and I would try to teach Kuba not to
bite so hard with saying No!  and pushing him away.  Now, I tell Katina to
take up for herself :).  She swats him when he nips too hard and he leaves
her alone when he realizes she won't be bullied.  It's important that you
discipline the cat from being too harsh with the ferret also.
 
Angel (1 dog, 1 cat, 2 birds, 2 ferrets, and a turtle)
[Posted in FML issue 2306]