Use castors tool
Data > NPC > NpcQuest.SData
Open that up, you make your NPC's in that (select tab for what type of npc)
the rest in that screen should be pretty simple for you
Adding NPC to your maps.
Again using Castors tool, open your map file
SERVER > PSM_Client > Bin > Data > Map
Pick the map you want (example: 18 for the 15 pvp map)
Use the little drop down list, and find "NPC"
Now, looking back at your created NPC, find the Type and TypeID (type can be worked out by looking at the other npc's in your map (1 = merchant, 3 = blacksmith etc.)
TypeID is like your item code, click "add" to put your npc on the map list.
Next you need to get the co-ords from ingame to add your npc into the map.
log into your server, run where you want, press "h" to find your x,y,z co-ordinates.
insert those in the "position" bit for your npc on the map, click add then set.. and voila
If you need more help, just ask
Credits to Castor for his amazing tool, and i think he wrote a guide on adding npc's aswell somewhere... :P