Offline plugin installation

I recently tried to install the acts_as_taggable_on_steroids plugin by
downloading the files one by one from
using firefox and saving them in a folder named
acts_as_taggable_on_steroids I then put this folder on a off line pc
and tried to install the plugin

C:\InstantRails\rails_apps\test>ruby script/plugin install E:
Plugin not found: E:\acts_as_taggable

As you can see I got plugin not found, after much hassle I decided to
connect the pc up to the net and entered

ruby script/plugin install

and this worked ok, its possible that I’ve somehow missed a file when
downloading the plugin manually, but I have checked it several times
and it looks ok, connecting up the offline machine for every plugin
that I need is going to be a pain so i would appreciate if anyone can
see any obvious errors in what I did for the off line installation or
if anyone knows of any software that can automate the download process
of getting these plugins?