Dont know if you figured it out already but its very simple, select an area, now in the landscape tab. select Exact in the choose operation box, do something like um type like 200 or something in the value box, click the change tab. Now go to Surfaces tab select the dirt texture (Eden\ps.paa), now you can either go to Edit and click "select all cells", or use Ctrl+Q to select it them. Once selected click the change button. Now go to the Flags tab and similar to selecting all cells youll want to "select all elevations" by going to Edit or usong Ctrl+W to do this. Once done click the Default button in the Flags section, Thats basicly it, you should now see yur terrain by using the the preview camera( F9 or under View).
Hope this helps if you havnt figured it out already.
Doe©