From what I've seen online it seems that for one reason or another they rarely if ever find the foot bones. I did find this article that addressed at least a partial foot of "Little foot", 3+-million year-old Australopithecine.
http://findarticles.com/p/articles/mi_m151...v17/ai_17915826Of course this information is now 11 years old, and maybe there's been newer evidence since then. One thing I found interesting was:
QUOTE
Until now the oldest evidence of bipedalism was the fossil footprints at Laetoli, Tanzania, which are believed to have been left 3.6 million years ago by A. afarensis. But last summer a team of paleontologists led by Meave Leakey, a member of the famed fossil-hunting clan, announced that they'd found a new species of human ancestor that predates A. afarensis by about half a million years. Leakey and her colleagues call the new hominid Australopithecus anamensis. The word anam means "lake" in a Kenyan dialect; the fossils--including some teeth, parts of the upper and lower jaws, an arm bonne, and these two pieces of a shinbone--were found near Lake Turkana in northen Kenya. The shinbone, or tibia, shows that the creature spent a fair amount of its time walking upright...
So there's another biped whom we have no idea what kind of structure their foot had... more apelike or more humanlike.