Spore Mech Parts isn't a Game or a proper Expansion. It is ideally a patch, but allows the use of 14 Special Mech parts for your Spore™ creations. It was released by Dr Pepper as a promotional pack, but you can download it free here: http://www.simprograms.com/dr-peppereas-spore-1-06-patch-and-14-mech-parts-download/

The website contains pictures and previews of the Mech Parts.