To Michie:
The Church teaches one baptism for the forgiveness of sins. The baptism is a Sacrament, and it leaves an indelible mark upon the soul. Fragmentofdreams is correct; as long as the baptism is done in the Triune formula, it is considered to be "valid."
The confusion often crops up if you are baptized in one particular denomination, and then decide to change churches. A baptism by one may not be recognized by another. For instance, if your first baptism had been performed at a Methodist church, and the minister poured the water on your head while saying, I baptize you in the name of the Father, and of the Son, and of the Holy Spirit, and then you later decide to attend a Baptist Church, there can be a conflict. Most Baptists believe in complete immersion. It is their belief you must be completely submerged in the water to represent your "death to the flesh," and then you rise up to represent rebirth into your new life. This is also done in the Triune formula, but the emphasis is on complete and total immersion. The Baptist Church says that sprinkling or pouring is not "valid."
In the case of the Catholic Church, ANY baptism that is done in the Triune formula is considered to be valid. Sprinkling, pouring, dunking, it doesn't matter. Just so long as water is used, and it is performed in the correct manner.
A side note: my sister-in-law was raised in a Protestant church, and was baptized when she was a teen, but she always considered the baptism to be something done for her mother's sake, it wasn't out of a personal commitment. When she later became Catholic, the Church considered her original baptism to be valid. But because of her feelings, that she didn't have the baptism to show her faith, but rather to appease her mother, she had a "conditional baptism." That would be sort of like insurance, I guess. "Hey God, in case the first one didn't take, here's the one I BELIEVE in."
I'm sure God understands.
Peace be with you,
~VOW