calling legacy COM local server from C# Web Service

[Flora Tang]

I have a C++ COM local server that interacts with a vendor
DLL. This COM server is made an EXE since the vendor DLL
dictates that each user connection be from a separate
process. I created a C# Web Service, added a Web
Reference to the COM server and a Web Method to new an
instance of the COM server and execute a method on it. My
problem is that after the Web Method finishes, the COM
server is still running (can be seen in the task
manager). I tried GC.Collect() to force garbage
collection but to no avail. Each Web client calls will
activate a new instance of this local server (which is
really what I want) while existing ones do not go away
even if the client was gone. How do I go about removing
COM local servers that are started by a Web service?

Many thanks!
Flora