Mike is spot on. Many eminent theologians put the actual date on or around 4 September 6BC.
Here's one for you...
Who was the Roman-appointed governor of Judea at the time of Jesus' birth?
And what act of unspeakable cruelty, according to the gospel of Matthew, did he commit upon learning of the birth of this new 'king' within his realm?
Given that this ruler really did exist (the Romans were detailed keepers of records), he could not have ordered the massacre of the innocents after his death.
So, if Jesus really did exist, he *must* have been born within the lifetime of this ruler who ordered his massacre, right?
So, when did King Herod the Great die...?
Even the God-botherers have had to accept this one, albeit grudgingly...
http://www.gci.org/jesus/date