kalinka-vinnie, you're right Halloween isn't a Christian holiday. The Christian holiday is All Hallows Eve. The word Halloween itself is a shortened form of "All Hallows Eve," the day before All Saints Day.
Take a gander at this, straight from the horse's mouth, as it were:
http://www.americancatholic.org/Feature ... efault.asp
My wife is more up on these things than I am, so I asked her. She said that this is a pagan celebration of the new year, which occurred now, not at the end of December. Between the old year and the new year was a between time, between two years, when the spirits could come forth.