My due date was December 24th and my daugthter was born December 26th. She is our only child so that Christmas was mainly focused on when she was going to come. However, in your situation I would just go on with your Christmas plans. If the baby comes before Christmas and you have already done your Christmas cards then just do a Christmas themed Baby Announcement. Don't worry about buying gifts for the baby, if you are concerned about it then take some of the items that you recieved with your babyshower or some items that you already have for the baby and wrap those.
Basically just if the baby is born right close to Christmas (like the 24th or 26th) then get some really cute pictures and that type of thing. I have always looked at my daughter as my late Christmas present and that is what she was...God's gift to me.
Also, with her birthday being the day after Christmas I also try to do 1/2 year party for her in June or July. That way she can have a birthday party with friends and such since it would be pretty much impossible to have a party on the actual day of her birthday.
Good luck and congratulations on your new baby to be.