You can still maintain your belief in Christianity, Islam, Judaism or any other religions, and still be a Buddhist. To be a Buddhist in the way Siddartha - the most famous of all the Buddhas -has it, is to realize the simplest truths about behaving, feeling, thinking, and living, and relating to human and non-human beings. Unlike other faiths, the Buddhist attitude does not cling to a set of beliefs; nor does it pass judgement on the beliefs of other religions. The Buddhist attitude has no quarrel with anyone who chooses to believe in any set of beliefs. The Buddhist attitude is primarily concerned with how one believes in, and practices, beliefs of his choice.
When Siddartha abandoned his princely life and headed for the hills to find the truth, it took him six long years to finally get on to the path of true living and being. During those six long years, he had experimented on the different ways of living and thinking, and believing. Each time, he failed and failed miserably. He must have had dabbled with what was described Philosophy. He may have had dabbled with the different sets of beliefs. Each time, he failed and failed miserably. After six years of failure, he finally discovered the path. He set foot on that path. The path was long. To stay on that path, the Buddha was required to question himself, his biases and prejudices, his ego centric ways, his long held philosophical beliefs. In other words, he had to question almost everything he had held dearly. In the end, he was rewarded.
Of the several fundamental truths about living, behaving, feeling, thinking and associating with human and non human beings, he discovered The Eightfold Path. These truths are not exclusively Buddhist because not only did he not create these truths, these truths apply to any human being, whether he be a member of a religion, an atheist, or a secularist.
Take some time to go over The Eightfold Path, and The Four Noble Truths.
