The origin of vampires really depends on how loosely you define vampire. It could include ghouls, zombies, etc.
Not to mention the various night demons. It's possible to find vampire-ish creatures as far back as Mesopotamian mythology.
As far as European vampires and werewolves are concerned, there are countless different versions of the mythology. As Gjallarhorn said, some cultures held that werewolves (and sometimes witches) became vampires after death. Others held that there were living vampires who would become a more powerful vampire after death. Furthermore plenty of cultures considered vampires, werewolves and witches to be largely the same thing.
Basically when it comes to vampire mythology nothing is simple
I always thought the vampire myths came from real life instances of people "coming back from the dead". Basically, medicine sucked back then, and so they'd sometimes bury people who weren't quite dead yet. Additionally, when people would exhume corpses, gas build up would cause weird noises and other unmentionables to be expelled from the corpse, giving it a rather ghoulish, half-alive appearence.
Mistaken death and death rattles etc are a common theory of the myth's origins. Also if a person is buried alive they're likely to scratch and gnaw in their desperation to escape, cue bloodied claws and teeth on a strangely fresh looking corpse.
Furthermore you have various illnesses such as rabies, anemia and haemophilia which are sometimes linked to vampire/werewolf mythology.
A friend once told me vampire lore could be based in ancient Scythia, though I've never seen any proof.
Scythian warriors were said to drink the blood and take the scalps of the people they killed (I'm not certain how true this is) perhaps that's what you're friend was thinking of?
