As this is my first theme, I don't know if these extras will be automayically installed into the correct places in order to work for the various addons.
If they are not, here's how to do it:

Snowcover:
*Move all folder inside 'SnowCover' folder to /Library/SC4Themes

Zeppelin:
*Move folder inside 'Zepellin' to /Library/Zeppelin

Colour Keyboard:
*Move folders inside 'Colour keyboard' to /Library/ColourKeyboard/Themes

All of the above can then be activated via the normal method for that tweak