RupertMurdock: I don't use porting kit, so I can't help you. But my personal guess is that the problem lies on porting kit's side.
As far as I understood your posts, Porting kit created a port for the game and downloaded the installer. When you try to install the game, the application cannot find the downloaded file and displayed the error message. Did you check your download folder whether Porting Kit downloaded a file?
I you want to use porting kit posting in their forums in the best option. (Or did you intend posting there but mixed up both boards?)
Some guys using MACs can help you here on GOG in case you would like to use wine. In this case creating a new thread or changing the title of this one might help.
it is literally asking me for a second installer! i need a second installer found in my mac in order to properly install the game.... so i downloaded gog galaxy as well just in case and still the same message comes up...