Testing different versions of components

Problem: Version management.

Description:

System Architecture:

Database Server (HOST) is Oracle, which is running on Digital Unix.

2 slave database servers also running(OPS), which are connected to
HOST, which are running on Windows 2000.

Client Application developed in Visual Basic 6.0, which are running on Windows 2000.

Business Layer (COM DLLs) developed in Visual C++ (ATL), which are running on Windows 2000.

2 COM+ Application servers are running.


Now the probelm is: There is a version of VTS3, which is basically is
PLC system and automating the production system. Using the source code
of VTS3, we have to develop VTS2. Remember that there may be a chanse
of modification in VTS3 also. Now while we are developing both the
applications, as on when we modify VTS2 or VTS3 we should be able to
test them through same client nodes. For that how to bulid our
network (servers, clients) and configurations.


How is this possible in case thik clients (VB clients).
How is this possible in case of thin cliets (while using CITRIX server).