I agree about the OPC server but not the link, I get to this place:
Orthodox Presbyterian Church (OPC) perhaps usefull to some but not when dealing with Siemens.
There are a lot of OPC servers. Siemens has all in "Simatic net" Cd. Im using it with an ethernet, but i used it with Profibus DP network, but with Visual C++ and Visual Basic. Simatic net cames with a OCX, if you can use OCX with Delphi, you are done. Apart from that, you can use National Instrumens Datasocket, is a OPC client too.