Humans have 46 chromosomes: 23 come from the mother (egg); 23 from the father (sperm). An egg without a sperm has only 23 chromosomes; it must be "fertilized" by the sperm to be endowed with all the genetic information (carried on the DNA of the 46 chromosomes) required for life.
All cells in the body are derived from this one fertilized egg. All the cells have the same chromosomes; the same DNA. What makes cells different is that different parts of the DNA are active in different cells. This activity is controlled by the activity of proteins and RNA (two things which are derived from the information carried by DNA).
The fertilized egg is a stem cell, but it's not the only stem cell. The fertilized egg divides into two cells and then four cells and then 8 cells. A stem cell can give rise to all of the tissues and organs necessary to make a human being. At a certain point, however, the stem cell becomes a "committed" cell. It can no longer make a human being. It can only make a certain type of tissue.
The "first generation" embryonic stem cell method of making a stem cell is to take an egg from a woman and fertilize the egg with donor sperm (actually a bunch of eggs, as excess embryos are typically created in in vitro fertilization clinics at the same time; the excess eggs/embryos are stored in liquid nitrogen for possible latter use). The fertilized egg is allowed to divide several times in cell culture, resulting in a little ball of typically 4 - 16 stem cells; in effect, the earliest embryo.
But stem cells are now able to be created using a "second generation" embryonic stem cell technology. Take an adult skin cell; introduce a small number of genes which direct the "committed" adult skin cell to revert all the way back to an embryonic stem cell; potentially capable of not only being used for stem cell research, but potentially capable of developing into a human baby, given the proper growth conditions.
This "second generation" embryonic stem cell would have the same genetic material and the same capabilities as a "first generation" stem cell. It would be the same cell as it was at the time it was a newly fertilized egg. It would genetically be an identical twin; a clone of the original fertilized egg, in every sense of the word.
But the cells are the same. In one case, the cells are created by going forward (fertilizing an egg). In the other case, the cells are created by going backwards (introducing a handful of gene to reprogram the DNA of an adult cell, so that the cell reverts back to the state of a newly fertilized egg). But the cells potentially are the same, with the same potential for developing into a baby.
In point of fact, it may well be that the first cloned human baby will come from this "second generation" technology and not from the "first generation" technology which everyone worries about. By officially sanctioning research into this "second generation" technology, the critics of embryonic stem cell research may actually be lending their support to a technology which has the greater potential for being used for a purpose they condemn (the cloning of a human).
Well, here it is!
http://stemcells.alphamedpress.org/cgi/reprint/2007-0252v1.pdf