Mary, the Catechism of the Catholic Church calls Purgatory a "state of purification" to prepare one for entrance into Heaven. Most of our concept of Purgatory comes from Dante's Purgatorio. I prefer the idea of purgatory presented in The Five People You Meet in Heaven, which is quite possibly more consistent with Catholic doctrine. I suppose Hitler and a few other truly evil people may be in Hell, but logic tells me that most ordinary people don't fit into the Hitler category.
-Joe Offer-