I have a product machine with oracle 8.1.7. data base is running. unfortunatly there is no orainventory directory.

I try to install some oracle intelligent agent.
universal insatller says there is no product installed this is first time installation ????
universal installer is looking for orainventory directory for installed product (which was remove by previous dba )

I donot want to disturb existing database.
I just want to installed intelligent agent for data gatherer services.

please help ?