This stuff is right up my alley, most of my work revolves around PLC's...
Profinet is the Ethernet equivalent of Profibus, so its basically an Ethernet wrapper around an older network system. Profinet is relatively new.
That being said, SNMP is not going to help you, SNMP may give you some diagnostics information on the Wago itself, but it won't give you the I/O status values. In order to do that, you will have to write your own Profinet driver, which believe me, is not an easy task.
The best, quickest, cheapest way to go about this is to buy an OPC server that can connect to the 750-370, then just write code to interface to the OPC driver. This is miles easier than rolling your own network protocol implementation.
Kepware OPC Driver for Wago 750's
You can then use free .NET API's from the OPC Foundation to develop your client.