Just thought I'd mention double fantastic. I was also having trouble finding the install directories of several pieces of non windows software as well. I changed the registry key this solution points to the the keys for that software and it works. Not only that but I pointed it at a bunch of random registry keys and it gave me their values as well
Edit just read the linked article about this method, from what I understood of it my use of this method shouldn't cause any problem but in case it does I should catch all errors and if this method fails to find the directory I can prompt the user to input the directory in a dialogue if its needed.
Thanks again for all the help