Timothy, I don't know if I ever discussed it with you, but even though I was raised and am a practicing Roman Catholic, I am of Jewish ancestry. With that in mind you can obviously guess that I am no stranger at all to Biblical Hebrew as the Church allows us to say many of our prayers in Hebrew, especially for celebrations like Chanukah (which is going on now) and the weekly observance of Shabbat (which with the Church, Hebrew Catholics observe from sundown on Saturday instead of Friday).
The Isaiah 7:14 subject is one that makes little sense if you speak Hebrew. The word in question (almah) is actually equivalent of the archaic English word "maid" or the little more modern word (but still out of use) "maiden." It identifies a type of person, not a description of the person's familiarity with sex. It can indeed be translated as both "young woman" and "virgin."
However the term "virgin" in modern English no longer means what it does either in Isaiah 7:14 or in Matthew 1:23 (parthenos) either. In both instances the term which Catholics traditionally translate as "virgin" applies only to a type of female. In modern English the word "virgin" no longer describes a type of person but a condition of a person, and modern English usage can apply "virgin" to both women and men (for example the popular comedy film of some years ago entitled The 40-Year-Old Virgin, which was about a man). Unfortunately it is this current usage that practically everyone you meet is using when they read these texts even though the term in both Isaiah and Matthew have little to do with a woman's sexual activity.
Both words, the Hebrew one in Isaiah and the subsequent Greek word in both the LXX and Matthew's text are used interchangeably throughout Scripture to refer to maidens, women who are at the age for betrothal with the connotation that such women usually wait until marriage before they engage in sexual activity (but it is only implied). For example, the LXX uses "parthenos" at Genesis 34:3 in reference to Dinah even though she had just had sexual relations with Shechem. This is correct since a "maiden" can still be violated sexually and still be no less of a "maiden" afterward since the words "almah" and "parthenos" just imply the status of what modern English calls "virginity" without making sexual status or lack thereof a requisite for the use of those terms.
In both Isaiah and Matthew the text is highlighting that the child to be born will bring God's presence. As Matthew uses it, he is stating the the Child to be born is to be God Incarnate.
But Matthew is also likely playing on words using what we Jews call "midrash." What we as Catholics call "Tradition," Jews call "midrash," and it is the official and often "oral" interpretation of inspired texts, with exposition or exegesis actually passed down with the way a Scripture text is read (like adding certain emphasis to a word or even using a synonym to highlight a variant way of translating something otherwise hidden in the original Hebrew of a text). Being that Matthew's gospel was written by a Jew for a Jewish audience, his readers would be used to "midrash" as a means to interpret the texts of the Tanakh in reference to Jesus.
Because the words "almah" and "parthenos" can also mean "a woman whose physical virginity is still intact," it is likely that Matthew's use of "parthenos" was midrash--one of the first examples of Apostolic Tradition or "midrash" to be written down. (For more information on this, see NRSV: The Jewish Annotated New Testament, page 4 in the box entitle "Virgin Birth.")
If one takes into account that Matthew 1:23 is now meaningless in modern English as "the virgin shall become pregnant" due to the fact that the modern non-religious reader could apply this to a man as well as a woman (a virgin man becoming pregnant would be a miracle too, some foolish people can now very well argue), we now see that no one on either side of this issue can expect a reading that will make English a perfect target language for these texts. English just isn't a good match for any of the ancient Biblical languages, and you have to admit that Westerners often expect things to match their preconceived ideas or be automatically counted as "wrong." So expecting even some very well educated persons to step out of using modern Western thought and deign to think like an ancient Hebrew may not go over very well. But a more accurate rendering for Matthew in our current sex-crazed world could be "and the virgin woman shall become pregnant," unless someone try to apply Steve Carell's character from that movie to the word "virgin."
For more information on Hebrew Catholics and links to various apostolates, see: http://en.wikipedia.org/wiki/Hebrew_Catholics
I hope you find some of this useful, even though I doubt it will stop native English-speakers/thinkers from their 2000 year-old-debate. It's really silly from the outside looking in.