That is the reason why Softwise has developed a SAP Proxy Generator to create proxies for SAP's BAPIS & RFC.
This code generator is a Visual Studio 2005 Add-in that creates the source code, in C#, to comunicate with SAP (based on SAP.Connector.dll).
But you can use VS2003 to create proxy files then move it to vs2005 and use it.
Here are vs2003 SAP Connector tutorial. Click me.
Code Snippet:
Destination sapDestination = new Destination();
sapDestination.AppServerHost = “SapServer”;
sapDestination.Client = SAPClient;
sapDestination.Language = SAPLanguague;
sapestination.Password = password;
sapDestination.SystemNumber = SAPSystemNumber;
sapDestination.Username = user;
SAPProxyClass mySAPProxy = new SAPProxyClass();
SAPProxyClass.Connection = Connection.GetConnection(sapDestination);
SAPProxyClass.Connection.Open();
SAPProxyClass.ourBAPICall(params); //Do some work here
