Marilyn:  as a fellow flea-fighter, let me offer this advice:
 
to get the fleas off your *fuzzy*, you need to get them out of the
*environment*.  i've found the best way to do this is to use a flea bomb
(take the ferrets out of the house for a day or so) -- as many as it takes
to nuke the whole house -- then to vacuum *everywhere* to get the flea eggs
(throw out the vacuum bag immediately), and flea bomb again 1-2 weeks
later, followed by a second vacuuming.  continue with the flea-controlling
baths during this time.
 
the bombing 2 weeks apart allows all the eggs that don't get vacuumed up to
hatch, and then you can kill the mature fleas (most flea bombs and sprays
don't affect the unhatched eggs) with the second bombing.  since we're
getting into winter, there shouldn't be much risk of new fleas riding into
the house.
 
this technique worked for me when we had bad flea problems a few years ago
-- one of my dogs had rubbed her back completely hairless (due to an
allergic reaction to the flea bites), and after the bombings and
vacuumings, the situation improved.
 
it's important to get all your pets out of the house for the time its being
bombed, though -- that stuff isn't exactly non-toxic.
 
good luck!
[Posted in FML issue 1050]