Quote from Jexius »Ignore what he said... he has no clue what he's talking about...
You need to install a mod to your server first, minecraft doens't have native support for mods yet.
Quote from TheBlackAcorn »
First get hmod it works with the npc plugin.
If you have problems installing that ask in the thread.
Then install iconomy 1.9 or above. There is a link in this post.
Then install npc's as per this thread.
If you have any questions post in the proper thread.
Quote from AliStarr
If you are using bukkit the the plugins folder should be created when you first launch the server. It is located in the same directory as the .jar and the launcher.