I feel that it is possible to help others without the belief that God exists. I am an atheist, and I've volunteered at the local hospital and museum of natural history, and I see no reason why this would indicate anything about my beliefs. I think that I am a somewhat selfless person - while I do care about my wellbeing, I care about others as well and am more than willing to help any who ask. For example, if a neighbor is moving in or out, I offer my assistance carrying their things, even if I don't know them very well. Being that I live in an apartment in a college town, people move all the time. Just yesterday, I helped someone remove spyware from their computer. There are a million little things like that I do for others, even though they offer little benefit to me. I just enjoy helping others out.
A roommate I had my freshman year was majoring in Philosophy. One day he told me about a subject discussed in one of his classes. He was asked the question "Can any act be altruistic?". He said that no act can truly be altruistic because you can think of a benefit to any given situation. While I suppose you can probably assign benefits to any act, I still feel that if you don't think about or consider those consequences while performing the act in question, the act is still altruistic.