In many neolithic / animistic cultures it is thought that the blood carries the vital energy of the body. This is why a person dies when a certain amount of blood leaves their body.
So it is thought that ingesting blood gives greater vitality.
I like katanas suggestion that a crossbow would be a good vampire weapon, if they existed, which I am sure is a fiction, at least in the Hollywood / Bollywood traditions.
I saw an old cowboy movie where the bad guy was a vampire and people could shoot him and he would not die. The hero figured this out, carved a cross into the head of one of his bullets, inserted a tiny wood cross and ended the menace.
Speaking of weird, anyone seen the India version of "Thriller?" There is also a Philippine prisoner's version.
I'll post the English subtitle version for those who do not speak Hindi.
http://www.youtube.com/watch?v=TtJRNyPK-lc
And for our Pinoy contingency ...
http://www.youtube.com/watch?v=o5nZcFIf3qc