gcf are files used by steam for mostly valve games, they contain all the files for the games, ncf are simply used by steam to direct steam to the game's commen files
maps should work in the non steam version but i would download the steam version, you can download it from steam(i think) as long as you are using cracked steam (i personaly use steamup) otherwise download the steam version from this forum,that way you can garenty that the maps will work along with the countless mods for half life 2