I am planning to communicate with a Siemens S7-300 with PC. If i using Siemens Prodave software, what kind/model of CP card i need to use? Is it just connect CP card to MPI port in S7-300 CPU? Any extra hardware? Thanks.

 

With Prodave you can connect to the MPI port of the CPU, using the CP5611 or 5511 or a serial to MPI Adapter. I don't know whether Prodave can use ethernet connections to CPx43.

There is an open source alternative:
http://libnodave.sf.net
It can be used on Linux and windows, but does not support CPs 5611/5511. It does support CP343 and 443.