Do you just give it Vampirism x% spells and make the face look gaunt like a vamp, or is there a box to check that will make it look like a vamp?

Cabius,

If you look under spells, you should find one called Vampirism (100,75,50,25). Add this to the NPC's spellist. Although you won't see it in the CS, the next time you play the mod, the NPC will be a vampire.

Hope this helps,

Kroot