Warning - I freely admit to being an avid pro-lifer and view abortion as the rather gruesome murder of an innocent child, who's life deserves as much consideration as the mother who conceived him or her. That said...
In November of 2003, Bush signed into law the ban on partial-birth abortions. Six months later, a California federal district judge struck it down in Planned Parenthood v. Ashcroft and a NY judge did the same in National Abortion Federation v. Ashcroft. Both judges argue the law is unconstituitionl as it includes no exceptions for the benefit of the woman's health. After a few other judges with rather similar conclusions, the Supreme Court has agreed to consider the constituionality of a law with no protection of a woman's health (never mind the baby's!)
Though there's no statistical info on when this type of abortion is performed, but Ron Fitzsimmons, director of the National Coalition of Abortion Providers, estimates that the partial-birth abortion is usually performed on a perfectly healthy mother and a healthy child that is at least 20 weeks old.
Partial-birth abortions use a process called "dilation & extration" aka D&E. The procedure involves dilating the pregnant woman's cervix and delivering the child feet-first through the birth canal. However, while the head is still inside the mother's body, it is punctured with sharp scissors and the skull squeezed, allowing it to follow the body through the dilated cervix. (Try this on a dog, and you'd most likely be nailed by the animal rights activists.)
Fortunately, this procedure is easier on the mother than the previous methods, which for those interested involved inserting forceps into the womb and pulling the baby to part and removing the body piece by piece. However, either method reduces the chance the woman will be able to have children at a later date, increases the risk of breast cancer, and often leaves her emotionally scarred.
If you've had an abortion or are considering one, you might check out the Crisis Pregancy Center (http://www.pregnancycenters.org/). Whatever you are going through, they will love you, listen if you just need to talk, answer any questions, and help you find whatever help you need. And its completely free and confidential.