*nods* I think there's been discussion about using adult stem cells for quite a long time now - they're found mainly in bone marrow (where red blood cells develop). Trouble is, they can't get them to differentiate as well as those from a foetus - foetal stem-cells have the potential to turn into any type of organ in the body, whereas (I understand) adult stem cells are more restricted.
On the subject of cow kidneys... cows grow cow kidneys as well, and as I understand it they work pretty well, as well...