Hi Marsy... Purgatory didn't become Church doctrine till quite late (I have 1085 in my mind, but I could be wrong). The best book on Purgatory is Jacques Le Goff, The Birth of Purgatory. Another good book on early ideas on Purgatory is Alison Morgan, Dante and the Medieval Other World, which is specifically about Dante, but also has a comprehensive list of other early visions/accounts of Purgatory.
Also, Catholics do use a different Bible, insofar as some books which are canonical for Catholics are not for Protestants. If you want a Catholic Bible in English, it's the Jerusalem Bible.
The main biblical source on which the notion of Purgatory was built was 1 Corinthians 3, 10-15: 'By the grace God gave me, I succeeded as an architect and laid the foundations, on which someone else is doing the building. Everyone doing the building must work carefully. For the foundation nobody can lay any other than the one which has already been laid, that is Jesus Christ. On this foundation you can build in gold, silver and jewels, or in wood, grass and straw, but whatever the material, the work of each builder is going to be clearly revealed when the day comes. That day will begin with fire, and the fire will test the quality of each man's work. If his structure stands up to it, he will get his wages; if it is burnt down, he will be the loser, and though he is saved himself it will be as one who has gone through fire.' So the idea is that all those who build on the foundation of Christ will be saved, but those who have lived blameless lives will be saved directly, whereas those who have not led blameless lives will still be saved, but will have to suffer first ('as one who has gone through fire' - and fire is a key element of most early notions of Purgatory). However, no shuffling feet there!
I know I am obsessed , but I am thinking of canto 3 of Dante's Purgatorio, where there are two mentions of feet moving slowly... One right at the beginning of the canto (where it is Virgil, dragging his feet because he feels guilty at not having guided Dante better) and one is when Dante and Virgil meet the souls of the Excommunicate, who walk slowly, dragging their feet. Not sure if that might be relevant.
Hmmm... have just re-read thread (sorry - it has taken me a while to write this post!) and am wondering, if it's a Pope saying it, if it comes from the Bull (or whatever it was... bit vague sorry) in which the doctrine of Purgatory was put forward, rather than from the Bible. Would definitely be worth looking at Le Goff if you can get hold of it.