Mike,
I've never traveled with any of my guys on airplanes but know several who
have.  Some airlines do allow them to travel in carriers under the seats.
 Personaly I would *never* allow any living thing to be placed "in with all
of the other pets".  I've been led to understand that the temperature
regulation there is not that good.  Also the time spent in the hold can be
considerable on a long flight - what if the food and water were spilled.
 Ferrets are just too delicate and I'd worry too much about their well-being.
 
If I'm not mistaken there was a post on here several months back from a
traveler who did allow the ferret to be placed in the hold.  The ferret lived
but the description of its condition afterward was not good.
 
Call the airline headquarters if you have to.  Call several airlines if you
can.  If you find one willing to let you carry it on with you, be sure to get
it in writting and carry the letter/FAX with you when you check in.
 
Dick B.
[Posted in FML issue 1042]