Both. Many say it is a way of life but, I've been around Buddhists most of my life and they chant and give food to their spiritual entities. That sounds like a religion to me.
It is both, or none, it all depends on how you accept it. It's certainly not a "faith", that is one thing I can say for sure. The Buddha said that it was wise to question everything, including him. He also said rituals and offerings were pointless, but many of his supposed followers do them anyway. There's thousands of different ideas of what Buddhism even is. Some of those ideas definitely can be called religion, and some can only be called a way of life. My personal path is definitely a way of life, not a religion. I think the Buddha himself started a Sang which could possibly be called a religious order, but that's complicated, and could be discussed for years with no complete agreement by all who discuss it.
Buddhism is a philosophy, not a religion. You can be anything you want. But Buddha believed in a higher plane of existence, so if you are an atheist then I don't think you are also Buddhist. You may agree with some of the Buddhist beliefs but not all, in which case you admire Buddha but are not truly a Buddhist.. An atheist doesn't believe in anything, so I am not sure you can be an atheist anything and be semantically correct. But the beauty of belief systems is that you can think whatever you like and nobody can stop you.
It is most definitely a religion. Religion is "a personal set or institutionalized system of religious attitudes, beliefs, and practices", which Buddhism has. Gods and the supernatural are not main factors in whether something is a religion or not.
Check this video out on Zen meditation. http://www.youtube.com/watch?v=xAz_Jkmp0dQ
It answers your question quite well, in the beginning itself.
Yes you can be an atheist Buddhist. My advice is, don't focus on labels of "atheist" or "Buddhist". Learn from everything, expand your knowledge and understanding of life and grow!