Yeah, they include the 4pin 12V P4 connector with every ATX power supply as far as i know.
The 20pin or 24pin is what you should be concerned about. The newer motherboards use 24pin (BTX) which has additional 3.3V, 5V, 12V and ground. The 4 pin P4 only has 2x12V and 2xGround its something totally different.
From what i noticed on that 320W they do offer both, either 20pin or 24pin so you should be fine either way. Just make sure that you order the correct one for your motherboard.