Harrach is a well known surname, and was an old noble family. There's still a palais in Vienna named after them, and several members of Harrach branches in our phonebook www.herold.at
You might find more information through http://www.surnamenavigator.org/
Is there any information linking *your* Harrachs to Austria? Or rather to the old Austian empire (you mention the 30-years-war!)?