Thanks, Blue. It seems that there were quite a lot of conversions here back before my time.
There may be instructions in the tutorials section. Adding terrain is pretty straightforward. If you have Play the World, you can look at Snoopy's terrain or Teturkan's set-up in the scenarios folder. Basically, you create a scenario folder with an Art folder inside it, and then place the Terrain folder in the Art folder. Then in your custom .biq file, add the name of your scenario folder into the Scenario Search Folders section of the Scenario Properties tab.