If you find someone who can help you, I'm also interested. As far as I know the PC/PPI interface is a datacontrolled RS232/RS485 convertor with speed adaption. Most RS232/RS485 convertors are controlled by one or more control signals, thus unusable for S7-200. As far as I know the Siemens PC/PPI interface is the cheapest one with this functionality around. It's also easily obtained.
If someone out there disagrees, let us know. As I stated before, I'm very interested in this info.
Kind regards,
Jean Pierre Vandecandelaere