I am having trouble using script/generate. I am following the tree based navigation tutorial, which says to use script/plugin install git://github.com/rai
Rails 3 is your problem (or rather the cause of). Since rails 3 all of the "script/whatever" commands have been replaced with "rails whatever".
So now you want "rails generate ..." or "rails server" instead.
Be sure to watch version numbers or post dates when looking at tutorials :) linkage: Missing script/generate in Rails 3