Interesting thread. I think the title is a misnomer though, because I don't think ytterbiumanalyst is suggesting that "just about everything in Christianity has pagan roots". There are certainly things which I think are "purely Christian" in Christianity, for example, the Incarnation (the basis of our Christological dogma) was a breakthrough of Eternity into human history and therefore connected with nothing experienced in human history before or since. On the other hand, the Church has the mission of sanctifying the Cosmos, and as such, she can (and has) sanctified customs which have pagan origins.
I think OzGeorge just "nailed" it!
The argument that a lot in Christianity comes from the Old Testament and is therefore
not "pagan" is very weak, IMHO, because in fact most of the OT itself has "pagan" (polyteistic, natural religion) roots. Yahweh may well have been the pagan natural god of calamities like earthquakes and volcanic activities; the obvious motifs of "our" God vs. "other" gods in the Torah and in the Psalms are very "tribal" (i.e., again, "natural" religious motifs, motifs of "our people," esentially race, blood etc.).
The notion of the Logos, i.e. the rational Cause and Means for the mere being, the mere existence of everything becoming a concrete human being without ceasing to be the Logos -that, I think, is entirely new (and not, BTW, folowing directly from the OT, all of its messianic prophesies nonwithstanding), and that is uniquely Christian, not pagan.