It has nothing to do with the Ethernet card in your PCs. They all communicate via TCP/IP. Macs have shipped with Ethernet built-in since the Flood. Plug each computer, including the Mac, into your router via Ethernet and configure each computer via DHCP and you are good to go. If you want to access files among the Macs and PCs, enable filesharing and SMB/CIFS. When you get your Mac, the only help you should need will be found in the MacOS X Help menu.
