Heathen, cool your jets, I think you got something right.
The Catholic church does not teach the Mary did have sex, nor does it teach that she did not have sex, after Christ was born. She was a virgin before our Lord Jesus was born however, and she is blessed among women, as the bible states. You sound like you know your bible, please check out Matt 1:26 (I think). This is what the Catholic church teaches; she may have had sex, may not have, but the bible certainly alludes to the fact that she could have. A recent archialogical (an ossuary in Israel I think) find indicates that she may have had sex, and that Jesus had at least one brother named James. The inscription on the discovered ossuary reads something like, "James, brother of Jesus", or something along these lines. The only problem with this find is determining wether the Jesus inscribed is the Christ Jesue. Jesus, the name, as I understand it, was not an uncommon name 2000 years ago.
Have a good day.