We made use of Host Integration Server 2004 to expose the existing CICS application via a component called WIP (Windows Initiated Processing) http://www.microsoft.com/hiserver/techinfo/whitepapers/2004/processing.asp.  We get to import existing Cobol code that defines the parameters for the associated method which we will be calling.  Once complete, HIS generates a .NET Managed assembly, which we then create a remoting proxy, and implement this proxy within our Web service.  Hope this helps.