PL2303 cable - USb <->Serial

I was supplied by E.ON with an Energy Monitor. It had Windows software with it but I run Linux.
When I run tail -f /var/log/messages and plug in just the lead that was supplied with the monitor I get the following:

Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.452191] usb 4-1: new full speed USB device using ohci_hcd and address 8
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.745504] usbcore: registered new interface driver usbserial
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.745538] USB Serial support registered for generic
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.745597] usbcore: registered new interface driver usbserial_generic
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.745602] usbserial: USB Serial Driver core
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.816324] USB Serial support registered for pl2303
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.816409] pl2303 4-1:1.0: pl2303 converter detected
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.838966] usb 4-1: pl2303 converter now attached to ttyUSB0
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.839142] usbcore: registered new interface driver pl2303
Feb 15 20:26:47 norman-HP-G56-Notebook-PC kernel: [75182.839149] pl2303: Prolific PL2303 USB to serial adaptor driver

The serial end of the cable is an RJ45 plug with either pins 2 and 5 or 4 and 7 connected. If you look at the plug with the cable coming in from the bottom and the face without the latch on then it is Red on pin 4 and Green on pin 7.
No other pins are connected.
A google search gave among other results : Prolific Technology Inc. (USB to UART / RS232 / Serial)

What I am building at present is a device with an Atmega328 chip having arduino bootloader and a sketch loaded, i.e a bare minimum arduino. it occurred to me that it might be possible to use this cable with my project to upload a modified sketch.
As it only has 2 wires on the serial end I do not know how this could be done so my question is can this be done or can I at least talk to my project via the IDE's serial monitor?

Had a much closer look at the cable with a magnifying glass and there is a third wire - rather pale yellow on pin 8.
So I am thinking now that I can hook up to Rx and Tx but need to find out if I can now feed output to the serial monitor.
Any ideas guys?

Looks like it - there are PL2303 cables for sale that say TTL serial interface, drivers for all major OSes - you've just got to figure which lead is GND, which is RX and which is TX - multimeter?