Hello Fritz;
You can use a CP1613 as PLucas suggests, in which case you will need a S7-1613 software license; you can also choose a standard (3COM type) network card, which will require a Softnet-S7 license. Both these licenses allow S7 exchanges between the network card and the S7 partner (in this case WinCC). The Softnet solution is cheaper, but will interrupt the PC processor every time there is an exchange over the network: it can cause a slowdown of the processor. Remember WinCC is very hardware intensive; a slowdown will soon become evident. If you can live with this aspect, choose the Softnet solutioon. If the spplication is time-critical, go for the Hardnet card (CP1613).
Contact your local Siemens rep. to get the part numbers and cost of the CP1613 and the required licenses.
Hope this helps,
Daniel Chartier