How to connect extra mouse and keyboard?
To connect additional mice and keyboards use USB-ports. If you don't USB-mice and keyboards, you can connect conventional PS/2-mouse and PS/2-keyboard by using the USB-PS/2 adapters.
Advice. You can buy a wireless keyboard and mouse to reduce the number of wires and get additional benefits of mobility. If you additionaly add a wireless USB graphics card, you will get a fantastic capabilities!