The virgin birth, do Christians really believe it? The answer is yes. And in many ways it’s a funny thing to believe in. There is no major Christian doctrine that depends on it to be true, (like the death of Jesus does), but we still believe it. Why if it doesn’t make a difference to what we believe, do we believe it? Because it is true, it is reality, the historical documents that we have of the time record it as a fact. (For an article on the reliability of the Bible, check out http://christianity.net.au/you/can_i_trust_the_bible and for the New Testament in particular, http://christianity.net.au/you/is_the_new_testament_history)
I admit that virgins don’t give birth every day. But neither do dead men rise. They are recorded partly because they are out of the ordinary. And yet both miracles are events that the authors of the New Testament unashamedly report. Now, we can either approach these events objectively or with a view like ‘miracles just don’t happen’. However, this sort of approach has little to do with empirical scientific method, which examines the evidence in reflecting on reality, and more to do with a philosophical prejudice.
Christians reflect upon the evidence provided in the New Testament documents and determine that such things as the resurrection of the dead actually happened. They represent the best explanation for the evidence provided in the New Testament, as well as other ancient documents, let alone for the history of the world (as reflected in the growth and development of the church). (See http://christianity.net.au/you/did_jesus_rise_from_the_dead for a defence of the resurrection of Jesus). Once a Christian trusts that the New Testament documents are historically accurate, and that they convey a truthful account of what they are describing, trusting them in their account of the birth of Jesus to a virgin becomes a simple task.
I recommend you have a read of one of the accounts of the life of Jesus, I recommend giving Luke a go (it is the one most concerned for arguing from a historical position). But when you read it, are you going to be honest with yourself and suspend any prejudices against miracles occurring? It’s no skin off my nose if you do or if you don’t, you need to be comfortable with your reading of the evidence, whether you’ve been fair or not. Remember reality can only be that which has happened, either it did happen or it didn’t. Read Luke’s gospel and work out which is more reasonable to believe.