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http://www.gaiaonline.com/guilds/viewtopic.php/?t=20487041&page=last&_gaia_t_=5844
http://www.vampires.be/index.php?title=Vampire_Anime_Series
http://www.amazon.com/Vampire-Anime-List/lm/R1Y4MVY26ACMTL
These are more general in topic, but the series you are looking for might be there:
http://en.wikipedia.org/wiki/Category:Supernatural_anime_and_manga
http://en.wikipedia.org/wiki/List_of_fantasy_anime

Okay, so I saw an episode of an anime six years ago when visiting Portugal (and therefore had NO IDEA what was going on or what the title was). The bits I remember are a boy being turned into a vampire (I'm pretty sure that's what happened anyway...) and being restrained by another guy who had orange hair and a green tartan poncho (or coat. possibly.) who was using silver thread or string.
And then some guys in futuristic white lab-coat-radiation-suit-hybrid outfits appeared which completely clashed with the old-church location and feel of the anime. Closing credits were just focused on one girl, I think.
I'm pretty sure it was made early 2000's, possibly late nineties. This has been bugging me for years, literally, if anyone can help me find out what it is I'll be immensely grateful