If it is a true cold (a rhinovirus) then ferrets don't get those.  They
DO share two thing with humans which people can confuse with colds:
bacterial sinus infections (which are very commonly mistaken for colds),
and influenza (which can appear like a cold if mild).
 
Lump on tail: read up on chordomas at
http://www.afip.org/ferrets/index.html
to see if that looks like what you are seeing.
It may be down for maintenance today
More info: http://fhl.sonic-weasel.org
[Posted in FML issue 4411]