This is the easy one. Switch on/off your loads connecting your arduino board to a relay board like this one:

You can switch on/off up to 8 loads each within this limits AC 250V/10A or DC 30V/10A. Connect arduino pins from 2 to 8 to the relay board channels 1 to 8 and also VCC and GND arduino pins to VCC/GND pins

See hardware  in Dealextreme

To install on your computer see How to Install Drivers
arduino firmware: StandardFirmata-2.3
skeleton file: switcher_sk.xml

Switcher Control

Customize your device editing skeleton file and change "SOCKET 0X" for the real name of the device plugin