Can you be an atheist and a buddhist at the same time? Sure. The words "atheist" and "buddhist" are only labels. Apply the labels however you see fit.
I'm sure I've upset a couple of people with my opening statement. Good. That means I have made you think. Let's dig a little further. Forgive me if this rambles as I am freeflowing this between mini-fires that flare up at work. Not real fires, but mini-IT problems.
What is an atheist? An atheist is "a person who denies or disbelieves the existence of a supreme being or beings." Source: http://dictionary.reference.com/browse/atheist
What is a buddhist? A buddhist is "One who accepts the teachings of Buddhism." Based on that description we need to ask what buddhism is. That can be one big old can of worms you may not want to open. What does our source say? "1 - The teaching of Buddha that life is permeated with suffering caused by desire, that suffering ceases when desire ceases, and that enlightenment obtained through right conduct, wisdom, and meditation releases one from desire, suffering, and rebirth. 2 - The religion represented by the many groups, especially numerous in Asia, that profess varying forms of this doctrine and that venerate Buddha." Source: http://dictionary.reference.com/browse/buddhist
Let's compare. Atheist - Doesn't believe in a supreme being(s). Buddhist - Doesn't believe in a supreme being(s). I see a similarity here.
The problem I have found is that there are many forms of buhddhism and some acknowledge higher beings and/or gods. On a positive note, the buddhists I have met in life are more open minded than the people I've met of other faiths.
Where do the two come together? How can we live as both atheist and buddhist? It's a matter of personal opinion. Look at the form for joining this community. One of the questions is about which faith you left to become atheist and buddhism is one of the choices. That may be true for a lot of peopel but I don't think it holds true for everybody. Again, it's a matter of personal opinion.
There are a lot of good teachings, humanist teachings, in the various forms of buddhism. Karma? I don't believe in it. Life is what life is. You make your own destiny and carve your own path. I don't see a problem with taking advice such as "Smile, breathe and go slowly" and adapting it to my every day life though. I know if I approach a tense situation with a smile, not a smirk, I am breaking some of the tension and helping all involved move forward.
What if we try to look at the eightfold path from an atheist (dare I say, humanist) point of view. I am taking these at their most basic meaning based on their titles.
1 - Right view: Everything and everybody will suffer. Find the things you can do to alleviate suffering for yourself and others.
2 - Right intention: Be a good person. Don't set out to hurt others, help where you can.
3 - Rigth speech: Words hurt. Ask anybody that has been in a loving relationship and had a fight. Think about what you say, why you say it and what may happen.
4 - Right action: This goes well with number 2. Be a good person. Don't knowingly do things to hurt others. Yes it would be fun to knock the office jerk on his ass, but nothing good will come of it.
5 - Right livelihood: This will very from person to person. An easy way to judge it is this: "Look at what you do. Does it make you happy? Do you finish the day with a clean conscience? If not, look into other opportunities." Maybe working at a slaugther house is ok for you. You eat meat and don't see a problem with it. Maybe you work at a slaugther house and leave each day feeling guilty. Only you can tell.
6 - Right effort: Where are you putting your engery? Where do you devote yourself? This is one that greatly varies by person. Think about it. Here's an example from my own life - Are you trying to reach level 80 with your Rogue while your wife goes to bed alone? This year makes 11 years of marriage for us. We're both happier if we go to bed together. Neither feels ignored.
7 - Righ mindfulness: Negative thoughts lead to negative actions. The next time you find yourself mad at something do three things: 1 - Stop everything you are doing. 2 - Take three big and deep breaths. 3 - Smile for 60 seconds. You will find yourself in a happier mood and the "not so bright" thing you were thinking of doing? You won't do it now.
8 - Right concentration: Where is your attention? Are you really reading this post or are you just scanning it and thinking of what's for lunch? Put your mind completely into what you are doing. (Says the guy writing this between mini-IT emergencies).
Hopefully at least 1 person will read my ramblings and go "Hmmmmm. I need to think about this."