What kind of communication port are you using now to communicate from the S5 PLC to the PC?
For example, if you are using a Profibus connection you must have a CP5431 FMS/FDL communication processor in the S5 PLC rack, so you need a CP5613 PCI board installed in the PC. With this conditions you can use the the WinCC communication Driver "SIMATIC S5 Profibus FDL" with the channel unit "FDL (CP5412/A2-1)".
On the other hand, if you are using the port AS 511 on the S5 PLC you do not need additional communication boards in the PC. In this case the communication is set up via either the TTY port in a PG or using the COM port on a standard PC. In the latter case you need to use an additional port converter in order to convert V.24/V.28 (RS232) to TTY.
You will find more information about the communication between a WinCC station and a SIMATIC S5 PLC in the online help.
We are using ethernet network communication (h1 cp143) for exchanging from the S5 PLC to the PC. Is it possible using normal networking card or need special cp card?
According to the WinCC Information System you need to use the CP1613 communication module in the WinCC side in order to communicate it with the S5 PLC via ethernet, so I think it is not possible using normal networking card.