I've always been fascinated with the first few chapters of Bereshis. Well, really, who hasn't? Within a few pages we go from God alone in the... well just alone, to the creation of everything, to the rise of man and then his fall and expulsion from paradise. Although the text is terse and keeps details to a minimum, the potential hidden behind the simple words is huge. Indeed, the ongoing debate between those who would take the text 100% literally and those who would interpret it in a deeper fashion is raging more today than many times in history.
For myself, I believe the world is 5769 years old as of three weeks ago. However, understanding that for God nothing is impossible, including creating a version of time that doesn't correspond to our current notions of chronological measurement, I also have no problem with the concept of a universe that has been around for billions of years. Remember that for almost the entire first six days of Creation, the only being wearing a watch of any kind was the Master of the Universe. What kind of presumptive arrogance is it that presumes that His Timex measures seconds the same as mine?
Thus the belief that a day in God's reckoning could take billions of years in ours is not beyond comprehension. I also would suggest that this is an important concept and secret of Creation that would allow many who currently insist on denying the principle of creation ex nihilo because of the difficulty they have with the strictly literal version of the text.
Consider the wording of the text: there was evening, there was morning, day X. How long was the evening, and what happened to the intervening nights and afternoons? A reliance on a translation or a simple understanding of the words robs our understanding of the text. Remember that Hebrew has a great flexibility for interpretation. Erev not only means evening, but also mixing (cf. erev rav=the mixed multitude). Bakar not only meaning morning but also is a root for one of the forms of clarification. The text might mean "there was evening, there was morning" or it might just as easily be implying "things were indistinct at the beginning of the process of the particular day and by the end eveything that had occured was clear".
However, I do not mean to dismiss the literal meaning of the text as an unacceptable way of understanding it. One of the core principles of Judaism and the foundational truth of reality is that God is omnipotent. While many of us are uncomfortable with the theory of the "already completed world", that is that God created a world that looked billions of years old so that all the conclusions of scientists regarding the true age of the Earth and its environs are completely wrong, one cannot argue that it is impossible.
The Gemara tells us that certain things should not be studied because of the adverse consequences such study brings about. One of them is to inquire into Creation and what came before it. Given that none of us were around at that time, nor could we hope to understand the scale of it, it seems sensible to conclude that a rigid, single view of how the universe was created is unlikely to convince all believing Jews. Yet, if one is flexible, there really is no core disagreement between the two versions noted above. What is most important is to accept and know that 5769 years ago, however that time is measured, God created everything we have. "The secret things are for the Lord our God", we said in Nitzvaim a few weeks ago. Our job is to live the most moral lives we can without creating ideologies based on unprovable suppositions that have nothing to do with the basics of our faith.