How do I install a Theme in Keynote? I just downloaded several themes that I want to use. They are in /Library/Application Support/Keynote/Themes/ but I don't see them in the Theme Chooser screen. 

Does anyone know what else I should be doing to install them?

Thanks!
When you open a template or a common keynote file, you can use the option File → Save theme...
This puts your file in the necessary directory automatically and adds information about your theme to the welcome screen.