The new cables are 1.1 mm. I don't know what the old ones are. You can use the new ones without a problem. I think on some you may find that the cable end is a bit too big to fit in your Campy DT shifter. You'll have to file them down a bit.
If you want to have that "C" on the end of the cable looking at you through the shifter, you'll need to get Campy cables. They also have the smaller cable end to start with.