For example, you can create a new type of NPC, let's say HamSandwichVendor, and make a file named HamSandwichVendor in data/npcs/, which explains his default health, alliances and stats.
Then go, in your level definition file:
data/npcs/HamSandwichVendor 100 100
To spawn him at 10.0, 10.0. And it even works from the console. [grin] Properly designed code is the booyah. I also added in a hack to take additional arguments, should you need to create a very special type of NPC that processes some additional arguments.