posted on Apr, 18 2011 @ 10:50 AM
While the existence of such things is highly debatable, you can really only go from the folklore.
For vampires, there are two main types...the American or European, again, depending on the folklore.
In American folklore, the vampire was more of a spirit than a physical being. The spirit would rise from the grave and take vengeance (usually on its
family), and then the corpse could be found with blood out of the corner of it's mount, etc. Most think the stories originated from improper
understanding of the process of death (i.e. bloating of gasses pushing out fluids, etc.) The stake was used as an elemental anchor to keep the spirit
in the grave. For destruction, the head had to be removed, and burned on a separate pyre than the body (and usually the head was stuffed with flowers.
In this idea, one could become one by being wronged, then dying, so don't think you want that.
In European folklore, it's more a physical being that could be harmed by stakes or silver (again owing to the elemental idea), but probably stemmed
from a lot of the same reasons above. To become one, you had to be bitten by one three times. Like the werewolf, there are also demonic rituals said
to impart the "gift" of vampirism, in folklore, so another route.
In more modern, fictional (only in that there is no folklore basis) accounts, vampirism is from drinking vampire blood, dying with it in your system,
and coming back.
As for demons, they are distinctly different creatures, so no folklore supporting becoming one, no moreso than there is for turning into a cockroach.
Two completely different things.