If you have installed X windows, you will see this installation screen. You will be asked:
Do you wish to configure X at this time? 1. yes 2. no >
If you answer '1' or 'yes' you will be sent to the 'Xconfigurator' program to configure and test your X windows setup. If you answer '2' or 'no' you will see this:
You can do it later using the command 'Xconfigurator'.