Hi Senator60,
I thought I would reply up here, just in case someone else runs in to this problem later on down the track.
To connect the RSE/DVD player video signal in to this plug, you will need to modify the Series I video connector for the old Headunit.
Luckily this isn't too difficult.
What you will need to do is solder / add an RCA Male connector to the Series I Video Connector wiring loom.
(Your best bet is to go to a $2 shop, and source a cheapy RCA audio extension lead for a couple of bucks,
and cut one of the plugs off with a decent length of wire to connect up to the cars wiring)...
The wire colours for the Series I Video connector can be found here. (Just for reference).
view_doc.php?doc_id=67&model_id=19#4(Just scroll right down to the X7 connector)....
Now here is where things get a little bit difficult.
You will notice that there are two red wires used on this connector.
One is for the RSE/DVD signal, the other is the RED Colour Signal for the Sat Nav System.
Now,
If you remove the tape wrapped around the Series I video connector (in the car) to expose the wires, you will find (after unraveling around 8 to 10cm),
that the 2 RSE/DVD Video Wires will split off from the 5 RGBs Video wires for the Sat Nav system.
(This is the easiest way of working out which red wire to use)...
Once you have found this pair, then connect the inner core of the RCA lead to the Red DVD Video Wire,
and connect the outer shield to the White wire (With a black stripe).
Finally, connect the newly added RCA socket to the above RCA video plug (The black one from memory, though I am not 100% sure),
and test the video by selecting the AUX DVD/RSE Input on the IQ system.
Unfortunately, I didnt take any pictures of this when I did it on mine, but I did something very similar when I fitted the reverse camera.

In the above image, you can see a white RCA plug at the bottom of the image.
I cut the wire, and stripped it back, and connected the inner core to one wire (brown in this picture),
and the outer shield core to the White (with brown stripe) wire.
let me know if this makes things any clearer for you.
Cheers
Matti