No, it wont effect the other port at all. You will need a switch or a cross over cable to hook up too it. By default the plc should have bootp on and with no IP address selected. Run the bootp server, wait for the bootp signal to pop up on the server, click it, assign it an IP (one that is in the subnet of the computer). You will need to add the ethernet devices on rslinx and assign the IP to a node on the configure drivers secion in linx as well. If you want to set the slc to auto negotiate, or to change its speed or duplex, you will need to power cycle the plc. This isnt need to just assign it an ip. This is the best way to get to the slc since your using the rs232 port for the PV.
matt