If you have a Windows XP:
You can go to USER > DOCUMENTS > Mount&Blade Warband > SceneObj
Windows Seven:
LIBRARY > DOCUMENTS > Mount&Blade Warband > SceneObj
Copy the scene you want and paste it in PW4beta2 > SceneObj
Start the game, choose edit mod and the scene you want to edit will be there.
Obs.: If you have many mods installed, the PW scenes can be found in the end, scroll down and you'll see scn_scene1 to scn_scene9