Install from iso (no disc burn)

[Harry Putnam <reader@newsguy.com>]

I'd like to try installing debian from an iso file but not burn a
disc.  Google turns up actual piles of reports and instructions for
doeing that, but as I plow thru I'm finding they all (so far) seem to
expect the user is installing debian on a windows machine.

I'm already running a linux machine.  I want to install on it.

Years and years ago I was able to do that on redhat... but I haven't
run read hat for something like 10 years.

Can anyone direct me to some documentation that does not assume I'm
installing from a windows machine but spells out how to plop a debian
iso somewhere, reboot and install from it when the machine is already
running debian.

Or any other way to proceed without burning a disc.  Or running a live
cd or etc.  I have no cdrom available currently. 

Some one is sure to say... why not just upgrade?

I don't want to take that route because my current debian box suffers
from months and yrs of major and ill-informed experimentation, massive
blunders and in general being piloted by a moron knowing just enough
to be dangerous.  It is in a sorry state at this point.

I'm convinced if an install from an iso with no burned disc is
possible it will prove easier and way less time consuming.