.net architecture

Question

Hi, I am re-engineering financial software and have the following design as of now. 1. Client in VB.Net -- Front End 2. Business Layer in VB.Net -- Middle Layer (Business Logic) 3. Data Access / Manipulation Components in Unmanaged C++ -- Back End Layer 4. Oracle 9i as database The client, middle and back end layer will communicate via XML. My query is as follows: 1. How will these components talk to each other in Dot Net Environment? Specially Unmanaged C++ and VB.Net 2. Will it be beneficial to develop the Unmanaged C++ code in Visual Studio 6 and remaining in Visual Studio 7, or all of them should be developed in VS7? The reason for using Unmanaged C++ is to get power of C++ with respect to data manipulation and collections using STL. Which book should I buy in order to get the idea of DOT NET environment at the same time focus on Unmanaged C++? Thanks in Advance Regards