this is the most controversial verse in the Bible, that I have seen so far.
Yes, the crux is in the translation of the word as ‘virgin’ or as ‘young woman.’
The Hebrew Study Bible, while maintaining the standard Jewish position about the meaning as “young woman” nevertheless says that it is puzzled that would be a “sign” as it is so common an occurrence. HSB does not allow the possibility that it is inclusive of the meaning of “virgin” even though the Jewish-origin Septuagint translates it that way.
This (amazon.com/Mary-Fathers-Church-Blessed-Patristic/dp/0898706866/ref=sr_1_1?s=books&ie=UTF8&qid=1370159944&sr=1-1&keywords=Mary+and+the+early+church+fathers) book and its second volume (amazon.com/Mary-Middle-Ages-Medieval-Theologians/dp/0898708451/ref=pd_bxgy_b_img_y) were written by a priest who researched and documented the development of the theology of Mary – and in particular, the perpetual virginity of Mary.
The development of this idea of Mary’s perpetual virginity has its roots in heresies that started in the very early church, either denying the divinity of Christ or denying his humanity. The fulfillment of Is 7:14 anticipates what is recorded in the gospels, about Jesus’ conception in Mary and his later birth.
The crux of that point is that Mary conceived Jesus in a divine way, not in a normal way by human sexual relations. So, her perpetual virginity is a consequence of the divine method of his conception and birth.
Following closely on the heels of the perpetual virginity of Mary is the related issue that Mary experienced no pain of childbirth – an idea that I had long ago dismissed as extreme piety towards Mary but – which is thought to be addressed by Is 66:7
Before she goes into labor, she gives birth; before the pains come upon her, she delivers a son. NIV (for example).