Step 1: Download
A plugin consists of a folder worth of files, with the folder having a name that ends with “.lrplugin”.
Installing a plugin involves simply moving the plugin folder to a place where Lightroom will find it, then restarting Lightroom.
Upon downloading, you'll want to unzip to create the plugin folder, then move that folder to the proper spot as described below.
Step 2: Installation
(The following applies to Lightroom 1.4 only. Lightroom 2.0 has different instructions. Skip to the bottom to see those.)
Installing on a Mac
You can simply click on it in Finder, and it will install for you. Cool.
To install either one manually, move the plugin folder to
/Library/Application Support/Adobe/Lightroom/Modules/
to install for all users, or for just yourself, to the folder of the same name under your home:
~/Library/Application Support/Adobe/Lightroom/Modules/
In either case you'll have to create the Modules folder within the Lightroom folder if it's not already there.
Installing on Windows XP
Move the plugin folder to this folder:
\Documents and Settings\username\Application Data\Adobe\Lightroom\Modules\
where username is your Windows username. Note that you may have to visit the Folder Options dialog to allow the normally-hidden Application Data folder to be seen.
You must create the Modules folder within the Lightroom folder if it's not already there.
As an example, on my XP system, the “COUTUREBOOK.lrplugin” folder ends up as:
C:\Documents and Settings\rodrigo\Application Data\Adobe\Lightroom\Modules\COUTUREBOOK.lrplugin
Installing on a Windows Vista
Move the plugin folder to this folder:
\Users\username\AppData\Roaming\Adobe\Lightroom\Modules\
Here, too, you'll have to create the Modules folder within the Lightroom folder if it's not already there.
Testing the Install
Restart Lightroom, select an image, then bring up the export dialog. Clicking in the top area of the export dialog should then bring up the newly-installed plugin in the list.
Uninstalling
You can uninstall or disable a plugin in a number of ways:
Delete the plugin folder, or move it to where Lightroom won't find it
Rename the plugin folder, for example, to “flickr.lrdevplugin-disabled”
Rename the “Info.lua” file inside the plugin folder (all plugins have an “Info.lua” file), e.g. to “Info.lua-disabled”
Lightroom 2.0 Installation
In Lightroom 2.0, navigate to File > Plugin Manager to bring up the plugin-manager dialog, click on the [Add] button in the lower-left, and navigate to wherever you've placed the “.lrplugin” folder for the plugin you'd like to install.