One product (I have not used myself) is SIMATIC Microcomputing. This is an ActiveX control that allows access to S7200 PLC's. You can then
use this in any container: Visual Basic, IE, MS Word, MS Excell, etc.
I believe that there is a modbus driver for the S7-200 included as an example program on the Siemens "Tips and Tricks" CD (which I think may also be downloaded from their web site). This is a program subroutine which you load into the PLC to allow it to talk Modbus. You would still need a Modbus driver of some sort at the PC end, but these at least are more common.
There is also a "free port" mode for the S7-200 port which allows you to create your own protocol. I haven't used this mode, but it is documented in the S7-200 manual (which you can download for free from the Siemens web site). In this case, you don't need any special drivers for the PLC or PC, but you will need to do a bit of extra programming.
**********************
Michael Griffin
London, Ont. Canada
**********************