>We have a similar process and it works in XP and Vista, we specifically install the app & updates to : GETENV("ALLUSERSPROFILE")\
That's a bad idea. Installing an application in a folder all users can write to opens a huge security hole on your customer's system. There's malware out there that targets EXE and DLL files, inserting its own code into them to do nasty stuff. They can only do that if those files are read-write.
Instead, do what MS recommends: install program files into Program Files (which is read-only in Vista) and data files to writable locations.
