In The Descent of Man, Darwin suggested that bipedalism evolved first in humans, which in turn freed the hands for other purposes, such as building tools. That seems feasible, but less than a year ago, Canadian scientists created a computer model which suggested that feet and hands might have evolved together at the same time, as there is a correlation between the proportions of finger length to toe length. The researchers used measurements from chimpanzees to work this out.
It's a fairly typical causation question: did our ancestors walk upright because they were using their hands all the time, or did they start using their hands all the time because they were walking upright? Or, as in any other correlation, did they evolve both abilities simultaneously? Over the thousands and thousands of years, it is so much easier to assume they did evolve "pretty much" together, but if we were to rewind to that period in our evolution, would one or the other ability be obvious to have come first? The study doesn't actually attempt to answer this question, as theoretically it's equally possible for a change in hands to result in a change in feet, and vice versa.
But common sense points out that it isn't possible to use hands much for tool building if they are engaged in moving. So bipedalism must have started evolving before the ability to use hands in more complex activities such as stone tool making. That is just a thought experiment, though, and until more definitive evidence is found, this subject remains debatable. What do you think?