Most resources you find will have origins in Buddhism. Ignore it. I'm an atheist too, and while I can't speak to the link above, look up Mindfulness in Plain English for another source that, while written by a Buddhist, is pretty much an "instruction manual" where you can just ignore every mention of spirituality and Buddhism (there aren't many of them beyond giving some context in the introduction). While I groaned once or twice (a mention of levitation...), the spiritual/religious content in that one is light enough that it should be easily tolerable for all but the most rabid hardline atheists.

It's available for free at urbandharma.org (there's a direct link elsewhere in this thread, that I'm too lazy to look up) or you can get a hardcopy from Amazon.