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If you wish to play in Snow Leopard OS X 10.6 / X.6 you will probably have the GOG version crash on startup. This is because the additions for GOG's Galaxy API crash the game as Galaxy doesn't work in Snow Leopard.

Go to your account and look at the Serial Keys tab(may need to be in a browser) for the game and

Go to and register the serial which will grant you access to downloads directly from introversion in the "Alpha builds" section(They aren't alpha builds now, that is merely a relic from the development build stage.) These will launch as they don't use the Galaxy Dylib(and they are DRM free like GOG's release).

NOTE - GOG will not likely give you support for this version but at least it's a work around.