SAP Enterprise Service Explorer
To me it seems that the SAP ES Explorer is the current textbook tool to connect .net in Visual Studio 2008 with SAP backend.
Can I use the tool only with an ESR on SAP side established, or also having just one WebAS ABAP. Since I have to configure the ESR I have not found a way to use it just with a plain WebAS ABAP.
for using the ES Explorer you need the ESR. Nevertheless you can also consume the Web Services from WebAS directly in Visual Studio 2008, we published a paper where we describe how to do this on http://download.microsoft.com/download/a/2/8/a287c141-b72e-4e9e-aac5-826e3f0d6d76/StatefulNetWeaverCommunication.pdf where we describe how to do it with Visual Studio 2005, the same approach works in Visual Studio 2008.