Does the Torah mean that there really was a "talking snake," or was it just a symbol of the Yetzer Hara (Satan/adversary)?
Rabbi Dr. Menachem Krakowski published an article in Hakira a few years back in which (along the lines of the Moreh Nevukhim) he interprets the entire story as a psychological allegory, including the man (reasoning faculties), the woman (emotional faculties), and the serpent (hedonic sexual/physical faculties).
Radak on Genesis 3:1: Excerpts below. Other points are in the link.
והנחש היה ערום מכל חית ה שדה אשר עשה ה' אלוקים
, It is in order to ask in what fashion the serpent conversed with Chavah. If G’d had opened the serpent’s mouth by means of a miracle, as He did when Bileam’s ass started speaking to him (Numbers 22,28), why did the Torah not report, as it did in that verse that “G’d opened the mouth of the serpent?”
The scholar Rabbi Avraham Ibn Ezra writes that the serpent did indeed speak, and it used to walk upright, just like man. Originally, G’d had equipped the serpent with superior knowledge and intelligence, i.e. “more crafty than any of the beasts of the field, but not as crafty as man.” this was also the opinion of our sages (Bereshit Rabbah 20,5) This is what they write: At the time G’d punished the serpent, He said to it: “here I had made you so that you are king of the all the beasts, something that you had not been satisfied with. I enabled you to walk upright just like man. You were not satisfied with this either. Now you will have to crawl on your belly and eat dust.” We must ask ourselves that if all this is so, why the Torah had not mentioned that the serpent had enjoyed such distinctions, that the Torah’s report of G’d’s creative activities makes no mention of this, as it did in Genesis 1,26 when man’s distinction over the other creatures is introduced by G’d saying “we will make him in our image, etc?” Furthermore, when G’d cursed the serpent, mention is meant of it having to crawl and having to eat dust. Why did the Torah not also mention that G’d deprived it of its superior intellect? This would have been the most severe part of the punishment and the Torah does not mention it at all? The most likely answer to all the points that we have raised is that the serpent was enabled, -miraculously,- on that occasion, to speak in a voice and language Chavah could understand, even though the Torah did not write specifically that “G’d opened its mouth,” as it did in connection with Bileam. seeing that this represented something far more extraordinary [Bileam’s ass speaking, which occurred in a world that was post Gan Eden, as opposed to an idyllic world where such miracles were not out of the ordinary. Besides, Bileam’s ass had saved her master from death by opening her mouth, whereas the serpent’s speaking had led to Chavah’s and her husband’s eventual death. Ed.]
Both approaches are legitimate and have roots in Orthodox litterateur.
Usually we refrain from interpreting the Torah as only a metaphor (see Rabad on Hilchot Melachim 12:1 and the Mirkavat Mishne there) , while in some cases we most understand the Torah in a metaphorical way (such as Deut. 10:16 "ומלתם את ערלת לבבכם וערפכם לא תקשו עוד"). However, interpreting an entire story is more problematic, and one shouldn't do it unless he finds it impossible to understand the story as it is.
The idea that interpreting certain parts of the Torah as metaphors is more problematic then interpreting prophecies (the dry bones prophecy) or certain books (Job and Shir HaShirim) as metaphors is explained by the Abarbanel in his commentary on Genesis 2:4 he states the main differences are:
Claiming an entire book is a metaphor is easier than saying that certain bits and parts of a book are a metaphor, since then you have to decide which parts are to be taken literally and which not.
Understanding dreams and prophecies as metaphors is easier and less problematic then interpreting stories that are documented and written its actual historical events as metaphors. Because then who can tell when it will stop? what prevents us from saying that King David, the Avot, even the story of the Exodus are metaphors?
This leads the Abarbanel to claim that even when the Rambam interpreted certain stories as metaphors, he did it only when he found it absolutely necessary. It should be pointed out that the Rambams interpretation of the story of Sodom as a prophecy or a dream, as he did with every story that involves angels, was not viewed as legitimate by all of the Rishonim. The Ramban even went as far as claiming (Gen. 18:1) that it is forbidden to read or believe in such ideas.
Nevertheless, the Rambams view is a legitimate Jewish view, which many Orthodox rabbis and sages have taken.
The bottom line is that if you understand the story literally you will learn a lot and will benefit, and if you want you can look at our different Rabbis interpretations to the story and learn as well.
אלה ואלה דברי אלוהים חיים
If you want, here is an article by (my grandfather, so I'm not exactly objective ;)) Rabbi Schubert Spero on the subject: The Biblical Stories of Creation, Garden of Eden and the Flood: History or Metaphor? - Shubert Spero