I found this useful blog while reading through a post on the Middle Earth DEM project forums, getting terrain into World Wind has always been a painful process, supposedly DSTile can do it, but only one or two people know how (and they have yet to write any guides).
So for anyone interested in getting custom terrain into World Wind check out http://wwterraintiling.spaces.live.com/ I am amazed at these guys patience and effort, great job Seer et al.
Dawn over Ephel Duath