I am still not sure what the problems is you are trying to solve, but I remember that we used to use USB View to trouble shoot problems with USB-RS232 converters on Windows XP.
It shows detailed info about to which port a specific device is connected and much more.
It seems that it is available for Windows 7 too, see
Map and troubleshoot your USB ports with Microsoft USB View[
^]
You can also get the source code for this software from MSDN. It is in C++, though, but maybe you can some idea about the missing link.
Not sure if this is what you are looking for.