How do vampires work?

If you actually monitor my all consuming panel on the left hand side of this blog somewhere, you'll see that I read quite a lot of vampire/werewolf novels. It was a natural progression from fantasy novels. I've read quite a few, if you ever want my advice on what's good and what's not, ask me.
What I don't get is how do vampires work? Now, different series have different types of vampire but in the whole they all agree on these points:

• Vampires are undead.
• They don't breathe
• They don't have a heart beat.

The undead concept baffles me but not as much as the whole "no breath" concept. If they don't have respiratory functions, how the hell do they talk? In the last episode of Buffy season 1, that episode when Buffy died for the first time due to drowning, Angel couldn't do CPR [due to lack of aforementioned breath] but he could talk just fine. How does that work? It'd be more logical if all the vampires have those machines that talk for them in monotone, but then that would shatter the image of mysterious, sexy vampires, wouldn't it?

Vampires' hearts don't work. So I assume they don't have a blood circulation since there's no pump to pump anything. So then what's the purpose of eating [ie. sucking blood] if there is no mean to distribute the nutrients [ie. some poor victim's blood] throughout the body?

I suppose logic and fictions don't mix that well.