Best tools/architectures for business systems

I have been asked to investigate various tools and architectures for 're- engineering'some of our business processes. The business processes are: 1. Billing system 2. Small contracts 3. Accounts Receivable 4. Sales We currently run all our business systems on an IBM mainframe ( :-( ) using ADABAS/Natural. We would like to implement a system with the following qualities: 1. Based on industry standards (Open Systems). 2. A logically integrated database. 3. A homogenous development environment. 4. Client/server architecture. 5. Optimal balance between real-time and off-line interfaces. On the client side, the platform should be a 386+ with VGA. The software should be MS/WINDOWS using some form of SQL interfacing standard. On the server side, the platform can be either a RISC-based UNIX system or a 486+ system. The software can be any database software (ADABAS/Natural, UNIX, Novell Netware, Oracle, Informix, Sybase). The interface should be SQL. In addition, the system would have to access/update data residing on the mainframe (ADABAS). We already have the following possibility: 1. Natural for Windows, ADABAS for UNIX. (However, this could lock us in to one vendor and this is not exactly a world standard. It would save on re-training costs, though.) Other ideas: 2. Visual BASIC for the GUI? Microsoft Access? Microsoft SQL server? Does anyone have any ideas, experiences to share with us? Any help at all would be much appreciated. Thanks in advance Merryl