YOu have to install it to Steam's CZ Deleted scenes folder, not the regular cz one
so put the files to steam/steamapps/whatever_is_the_ds_folder/czeror/maps and maps/graphs
edit: i've found this in the Steam forums:
Description: This was VERY hard to get working. The first thing you have to do was open up "condition zero deleted scenes base content.gcf" (I recommend getting GCFScape to do this). Go to the czeror sub-folder, and extract ritual_standard.wad, sandstorm.wad and turncrank.wad. Put them in your czeror folder (I mean, the actual one not in the gcf). Now you can start the map like how you start the Swamp map series (Load a saved game, then type changelevel rubble in the console).