Sick koi and need advice (with pics)

I have a koi with an unusual growth on its tail fin that looks like a
praying mantis egg sac. The fish also has hazy white areas on its
body. On its back there is a large opaque oval and I noticed some
smaller areas on its head. I first noticed issues with this fish in
the spring of 2005 and put it into a holding container with another
fish for several weeks as I dosed it with anti-bacterial and anti-
fungal medicines. It didn't seem to get better but upon closer look
it didn't seem like these white areas were disease, so I blew them off
as possibly an ugly batch of scales.

Now it's early 2007 and those white areas still exist and are possibly
larger but not substantially. The growth on the tail is something I
just noticed a few weeks ago and definitely is not healthy. I think
another of those growths exists on the underside of the fish near the
tail fin, but as you can imagine it's difficult to net and examine
this fish close up. The end of the fin itself seems to be diseased,
yet not in a way that would cause tearing.

If I had to take a guess I'd say this fish is at least 18" long and is
at least 2.5 years old and the other fish in the pond seem healthy.

Here are links to some photos:

The odd growth == http://s1974.home.comcast.net/sick_koi.JPG
The white region == http://s1974.home.comcast.net/sick_koi2.JPG

I have a feeling this isn't a bacterial infection, fungal disease, or
parasite because those issues should have spread to the other fish in
the 2 years that I've noticed odd health issues with this one. The
only other thing I can think of would be some sort of fish cancer, but
I'm not a vet so I have no clue.

Any ideas on what's going on? If so, what do I do about it?