>Should a Christian ceremony be held in a place sacred to pagan beliefs?

Yes, why not? I was there with my children and nieghbours. I'm not a Xtian or a Pagan but I don't mind what sort of God people choose to worship within the stones. Blokes in frocks calling an unseen diety to help them happens at least once a month here.
It was nice to see something that had actualy been organised with song sheets etc rather than the same old rituals that the pagans perform with regular monotony.
Personaly I don't think Avebury ever had anything to do with religion anyway.
http://aveburytour.mysite.wanadoo-members.co.uk/Xtians.jpg
PeteG