Question regarding the lore of vampires here. Are they supposed to be the classic undead version of vampires or are they instead afflicted with a form of disease? How is it they came to be? I want to know for role-playing reasons. If my character becomes a vampire, is he then technically "dead"?

If you become a vampire, then the game marks you as undead. Any spells, enchantments, etc. that effect the undead will now effect you. Many people take advantage of this fact by becoming a vampire and taking the necromage perk in the restoration tree to make their spells and enchantments more powerfull.