As Solatar posted above, there is no one "Christian" viewpoint on most religious issues. There are many sects of Christianity; for example, fundamentalist Christians would disagree with many of the doctrines that form the cornerstone of my Catholic life. What unites all Christians is the belief in Christ as the Son of God and Savior.
As for the question at hand, I'm much more in agreement with Solatar/ShadowWolf than Setekh. For example, as a Catholic, I do not believe that salvation is a matter of faith alone. What we do is as important as what we believe. In fact, someone who professes to be a Christian and lives their life in a manner contrary to the teachings of Christ really isn't much of a Christian, is he? If we claim to believe in Christ, we are obligated to follow Christ's teachings. As I mentioned, this is not a universal belief among Christians; indeed, Luther's belief in "sola scriptura," the principle that faith in God was the sole requirement for salvation, helped lead to the Reformation.
As for what I believe, and for what my faith teaches, I think it answers your original question Nico, at least in part. I believe that my own faith is the fullest revelation of God's truth to humanity. (Note that I don't expect a single one of you to agree, and I'm not offended if you don't. That's just my belief.) At the same time, however, the Church teaches that every faith has at least some aspect of truth in it. In other words, although people are of various religious beliefs, they are really worshipping the same omnipotent being of God. This may have been the position of the Church in the past, but it has not been for a long time. I personally believe that any person, no matter what their particular religious faith, can achieve Heaven. As some of you have said, dooming someone who has never heard of Christ to Hell for that sole reason isn't exactly the sign of a benevolent and forgiving God, is it? I believe that anyone, be they Christians, Jews, Muslims, Buddhists, Hindus, Sikhs, or anything else, can achieve salvation. In my mind, at least, if someone lives a good and virtuous life according to their particular faith, then they will go to Heaven.
If any of you have ever read C.S. Lewis's
The Chronicles of Narnia, a particularly wonderful children's story that is also a Christian allegory, this can be easier to understand. In this story, the character meant to represent Christ, the lion Aslan, talks to someone who worships a different entity, a god of warfare and terror known as Tash. This person has loyally worshipped Tash for his entire life and has lived virtuously. After the end of Narnia, in Paradise, the man asks Aslan, "For my whole life I have feared you and worshipped Tash. How, then, can I be here?" Aslan answers, "Any good deed you performed in the name of Tash was rendered unto me. Likewise, any evil deeds performed in my name were rendered unto Tash." (This is a truly excellent series of seven books; even though I first read them in second grade, they remain perhaps my second-favorite series of all time. The ending is particularly beautiful. I'd highly recommend them.) The point of this allegory is that, as far as I'm concerned, anyone who does right by their own faith is doing right in the eyes of God. This same concept even holds true for atheists. Yes, that's right, I believe that someone who does not believe in any concept of a higher power can get into Heaven, so long as they live a good life to the best of their ability. This belief might shock a few of you.

This is not the same as the concept in Dante's
Inferno; I'm speaking of the full actuality of Heaven, not a particularly nice level of Hell or anything.
The issue of unbaptized babies is one that has changed over the history of the Church. Even as recently as into the twentienth century, the Church spoke of the concept of "limbo," a state of being where babies who died in the womb or unbaptized would reside. However, this teaching has been somewhat downplayed over the past few decades. Personally, I believe that an all-loving God would bring all children, including the unborn and baptized, into His care.
As for those who died before Christ's crucifixion and resurrection, I'm not entirely positive of the specific Church teaching on this point. I personally believe, however, that, whether before or after Christ's death, the good who died before Christ was born did make it to Heaven. I'm sorry that I can't go into more detail; I will try to look it up, though. I'm also not entirely sure of Jewish beliefs regarding heaven and hell; I do know that certain people in the Old Testament are referred to as being in heaven, and Christ's parable of the beggar Lazarus details him being taken to Heaven. At the same time, though, Christ's death and resurrection destroyed death and enabled all of humanity to attain everlasting life through redemption. I'll have to get back to you on this specific point.
As for my own specific images of heaven and hell, I see heaven as a place of indescribable beauty and light, a state of perfect union with God. I see those in heaven as being like God, all-knowing and completely good. As for hell, I see it as a place of utter darkness, torment, and sorrow, a state of complete separation from God. I also believe in Purgatory, a state of purging one's earthly sins before one enters into Heaven.
I hope this post has done some good, and I hope even more that it doesn't start the oh-too-easy path to a flamewar.
