but the plug that you connect directly to the computer is already taken by the standard printer. How do I set up both?
You do not say what type of connection is required, Serial RS232, USB, IEEE 1394 (Firewire)? Also it would be helpful to know what make & model your "standard" printer is.
We can be more specific if you give us that information.
Most printers now normally connect to a computer with a USB connection; computers (unless very old) will have more than one USB socket.
Some printers use the IEEE 1394 connection, but often have the option of USB too.
It sounds as thought your plotter is using a serial RS232 connection (D shaped, multi-pin) as there is only one socket on your computer. Check whether the "standard" printer has the option for a USB connection.
Terry.