I don't know anything about Russion Orthodoxy but you're right that a Roman Catholic would (usually) beg to differ w/what Pellius posted because they seem to teach traditions and whatever they deem truthful at the moment over what the bible says. One of the popes even made Mary a "co-redeemer" w/Christ didn't he?
Some would say that Roman Catholicism (depending on the teaching) and Biblical Christianity are different things. I don't see how that makes Christianity "shaky" as you say.
Do you know a lot about Judaism? I'm interested in learning more about it (if you have time we could discuss it on the Relig. Board).
What I mean by "Shaky" is that nowadays, a lot of people tend to think of Christianity as unified concept where differences between catholics, prostestants, orthodox, apostolics, etc.... would only be of a kind of shade. Which is not only historically but philosophically and spiritually false. Actually, the only thing they have in common is their source. In fact, there are differences within those trends. When you think catholicism, you think Roman Catholics. But everybody should remember that one very strong part of the Catholic history is German (still now, Bavaria is the most hardcore Catholic practicing region of Europe) and that the Roman and German Catholics have fought for a long time (I'd admit that this was mainly a struggle for power and that their theological differences were few). Same thing exists within Protestantism and also other religions like Islam. As for Judaism, I've come to study it a bit though I was born muslim. I must say I deeply respect Judaism intelectually though I disagree with a lot of it.
