If anyone needs instructions for combining dual layer DDP files, here are the instructions i created a couple of years ago from terminal comands i found on the internet.
1.) Create a "Temp" folder on the "desktop" or your "Home" folder, somewhere that will be simple to access through the Terminal. If you decide to use a name other than "Temp" make sure it has NO SPACES unless you are a Terminal guru who knows how to work with them.
2.) Open the "Layer0" folder. Copy the "MAIN.DAT" to a Temp folder then rename it to "Layer0.DAT".
3.) Repeat step 2 with the "Layer1" folder.
4.)in the Terminal navigate to the Temp folder using the "cd" command. So if the Temp folder is in the Home folder all you would type at the prompt would be:
cd Temp
It should now look something like:
Computer_Name:~/Temp user$ []
5.) Now Type:
cat layer0.DAT layer1.DAT >> new.DAT
(there are spaces before and after the ">>")
6.) Once you know the file has finished, rename "new.DAT" to "new.img". Now you just double click it to open it. If the DVD player didn't already open you can now open the DVD with it or burn it to a DVD-R for testing.