Oracle Heterogen. Services & SQL Server

I want to link an Oracle 8/8i Instance/Schema to a SQL Server Database via the Heterogeneous Services. I have documentation which tells me how to do it, but it mentions an agent which needs to be accessed by the listener. What is this agent? Where do I get one, or does it come with Oracle? Oracle and Microsoft have been giving me a run-around on this subject.

If anyone who has done this before and can give me additional information (the stuff you don’t find in the tech docs), that would be greatly appreciated as well.

Thanks in advance.