Open the Sighthound Video web page.
Click on "Try Sighthound Video For Free"
You now need to login to your account, using the form on the bottom on the page.
Make sure your email is correct, and enter your password (I have mine saved, so it gets filled in automatically).
Then, click the "Sign in" button, which will open the downloads page.
The current releases are displayed, but you will want a previous version.
Click on the text "Looking for a previous version?" to expand the view.
Scroll down to find the version and platform you want, for example, "5.1.7" and Mac OSX.
Click the "Download Mac" or "Download PC" button to begin the download on the installer.
After the installer is downloaded, it can be used to install Sighthound Video.