SlideShowPro Player for Lightroom is downloaded as a compressed ZIP file. To decompress, simply double-click on the ZIP. When complete, you will see a folder named "Install" containing four folders: "Lightroom 1", "Lightroom 2", "Lightroom 3", and "Web Templates". You will move these folders as part of the installation process. If you run into problems unzipping the file, please see "Invalid archive after download".
The easiest way to install the extension is to let Lightroom show you where it needs to go. Launch Lightroom, and select "Lightroom > Preferences" on OS X, or "Edit > Preferences" on Windows. The "Preferences" window will appear. Click on the "Presets" tab, and look for a button that reads "Show Lightroom Presets Folder." Click this button. (See button in Lightroom 2 / See button in Lightroom 1)
Your operating system will open a new window pointing to a folder named "Lightroom". Open the "Lightroom" folder. You should now see a folder named "Web Galleries". Open the "Web Galleries" folder, or create it if it does not exist.
Now move that window to the side, and return to the folder you unzipped. If you are using a 1.x version of Lightroom, open the "Lightroom 1" folder. If you are using a 2.x version of Lightroom, open "Lightroom 2". If you are using a 3.x or 4.x version of Lightroom, open "Lightroom 3". Inside all of these is a folder named "slideshowpro.lrwebengine". Move the "slideshowpro.lrwebengine" folder to the aforementioned "Web Galleries" folder.
After you have performed the installation, please make sure the following files exist according to your operating system (there should be more, but this is just a start).
C:\Documents and Settings\
%USERNAME%\Application Data\Adobe\Lightroom\Web Galleries\slideshowpro.lrwebengine\slideshowpro.swf C:\Documents and Settings\
%USERNAME%\Application Data\Adobe\Lightroom\Web Galleries\slideshowpro.lrwebengine\js\slideshowpro.js * The "Application Data" folder may be hidden
Windows Vista, Windows 7, or Windows 2008:
%USERNAME%\AppData\Roaming\Adobe\Lightroom\Web Galleries\slideshowpro.lrwebengine\slideshowpro.swf C:\Users\
%USERNAME%\AppData\Roaming\Adobe\Lightroom\Web Galleries\slideshowpro.lrwebengine\js\slideshowpro.js * The "AppData" folder may be hidden
/Users/$USER/Library/Application Support/Adobe/Lightroom/Web Galleries/slideshowpro.lrwebengine
When step one above is complete, move the "Web Templates" folder inside the unzipped folder to the same "Lightroom" folder you moved "Web Galleries" to in step one.
If Lightroom is currently open, quit/relaunch the application. When relaunched SlideShowPro Player for Lightroom will be available in the Web area.