So, mostly idle speculation here. If Adam and Eve were created with an understanding of good and evil as "what God wants" and "what God doesn't want", then they would have been perfectly aware (especially seeing as God commanded them not to do so under penalty of death) that eating the fruit of the tree was a Bad IdeaTM.
It wasn't until the serpent came along that they started to doubt God (the serpent said God was lying to them IIRC) and eat the fruit. The command given to them was something along the lines of "if you eat it, you will surely die", which they didn't, so it probably means something else. The traditional interpretation is being cut off from God, seeing as after the fall he kicked them out of the garden and didn't really speak to them any more.
Now, this is where I'm getting really speculative, but if we were to reconcile this idea of spiritual death and the apparent lack of free will, could we not then say that free will is a product of a healthy spirit? This ties in nicely with the Reformed idea that nobody has free will (in the sense that they cannot choose to not do evil) until the Holy Spirit regenerates their... spirit. As in, makes it alive again.
Also of note is that (again, in my church's teaching, I can probably find some verses if needed) Adam was made to be the representative of mankind, and he had to make decisions on everyone else's behalf.
I'm also using the term "free will" to mean "the ability to make objective decisions by weighing up the pros and cons of each option". Of course, biblically, this would mean that the result of free will is always God's will, at least in terms of good vs. evil. Choosing between raspberry and blackcurrant jam is kind of a different story.
So, in summary, Adam and Eve had free will until God (or Satan, or whomever, I don't know) stripped them of it as a result of their death in spirit. All of their descendants (read: everybody) is in the same boat, until God makes you alive again, at which point you regain the ability to do Good StuffTM, which is pretty much regular good stuff, but done out of a desire to please God.