Hello, I am very new to skinning (I have done a few very basic skins) but I have come across a point where I am stuck. In the map_info picture of the XRG it shows where you can paint/skin etc, but when I paint an area the whole car gets painted. So say I painted the side of the car, the rest of it would get done too. This happens with the wing mirrors too.

Can anyone shine any light on the situation?

Are you using the 3d painting tool?
I suggest you go and use the MSz skin kits, they're mapped and have a black mask to show where you can paint.
Download them here

If you are using the skin kits then you've probably not selected the part where you want to paint.
There's several layers named with each part of the cars body in the skin kits. Hold down Ctrl and left click on the little preview of the layer you want to paint(in the layer menu bottom right). It should select the part you want to paint.
Then on a new layer use the fill/bucket tool to paint that part.

Thanks for you help