Nope you are correct.. EVERYTHING went to your / dir.
so anything you install is in your / dir.  All your
src files are in your / dir.  chances are  if you
installed all the sources for everything and you did a
full system install that is where the majority of your
room went.  look under /usr/local/src/ and /usr/src/
see how much stuff is in there that you don't need.
How much ended up in the /tmp file from the installs.
Another nice thing about seperate partions for things.
Easier to keep track of what is doing what.  Not to
mention the security that you get from it.
Also try du /var/log and see how much space is being
taken up by logs. I have had a couple of Mandrake
installs that would just keep piling up the logs. Kept
ending up with logfile names like
mail.info.4.gz.gz.gz.gz.gz.gz.1.gz.gz.gz.gz.gz.gz.gz.gz.gz.gz.
 well you get the idea.  
Only had that problem with Mandrake though.
Anyway, what I am getting at with all this useless
typing is, start with each subdir of your / partition.
Find out exactly where everything is.
Then get rid of the excess.  Or move it.

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