I've never used it, but in taking a quick look on the Siemens website, it looks like you need the WinAC ODK. Download the manual here:
http://support.automation.siemens.com/US/llisapi.dll/csfetch/19256518/WInAC_ODK_V4-1_e.pdf?func=csli...
Here's a description from the manual.
The Windows Automation Center Open Development Kit (WinAC ODK) is an open interface to WinAC
controllers. It provides a set of tools that enables you to implement custom software in C/C++ that works
with your STEP 7 control program for WinLC Basis, WinLC RTX, or Slot PLCs (CPU 41x-2 PCI.) These two
interfaces are the Custom Code Extension (CCX) and the Shared Memory Extension (SMX.)
It also provides an interface that allows you to implement a custom application in Visual Basis, Visual
C/C++, C#, or Borland Delphi 7 to get values from or set values in a WinAC controller for specific predefined
controller features. This interface is the Controller Management Interface (CMI.)
