There are many links to the origins of Christmas.. look at
http://www.christmas-time.com/cp-hist.html
for example..
But does this make it wrong to "christianise" a pagan event and create something holy and beautiful that honours God?
Paul said that as God created all things, all things belong to God. It is the created beings that have chosen to worship the created rather than the creator. So when paganism or any other form of worship finds it's truth in God alone.. then isn't the worship being restored to the one who deserves the worship?
Paul took the unknown God of the Greeks of Athens in Acts 16 and used it to bring the Athenians to God Almighty. When Christians celebrate Christmas, though it may have been an original pagan holiday.. it led the world to one time a year, and to think about the Lord Jesus. It showed how the truth of God had been exchanged for a lie, and restored the true meanings of Christmas from a satanic worship ritual, to worship of the one true God.
Unfortunately.. the one who lost the worship doesn't like it.. is it any wonder that a jolly old man named santa claus is an easier person to celebrate at Christmas than a tiny baby who will oneday grow up and die on the cross for them?