Rated 5 out of 5 stars

For those who can't install it, go to http://themes.mozdev.org/ and download the "Theme Installer" add-on. This will allow you to install a theme from a .jar file. Next, copy the SeaHawk .jar file to a location known to you (by right clicking the "Add to SeaMonkey" button and choosing "Save Link Target As"). Next, you invoke the Theme Installer via one of two methods (depending on the Theme Installer version)

1) Edit->Preferences->Appearance->Themes, click the "Install jar theme" button, navigate to the recently downloaded .jar file and click OK. Then follow the prompts.
2) Edit->Preferences and selecting Theme Installer from the Category pane. Then follow the prompts.

Once you restart SeaMonkey, SeaHawk should be in your theme list (View->Apply Theme).