Thanks for the reply, but no, I'm actually trying to get the address that sent the money. Later I will be sending money back to that address, kind of like bit lotto does (although I hadn't heard of bitlotto when I made this post).
To work you HAVE TO BE SURE that certain conditions are met: they only send the BTC running software on their computer and that they are still using the same wallet and haven't deleted it or moved on to a new one.