How many atheists actually understand science?

Atheists are just like anyone else when it comes to education, they don't all specialize in science. Just like anyone else they believe what they read if it fits what they believe. They don't believe in God, so any science that would make it look like there is not God, they believe, even without evidence.

Most atheists and most theists have at least a general understanding of science, some more so than others obviously. About the only people who reject basic facts of science are fundamentalist Protestants, who reject any scientific facts that don't agree with their misinterpretations of the Bible.

born again Christian biologist

More atheists than Christians, certainly.  The scientific nonsense we see here proves that most fundamentalist Christians don't even have what's expected of a high school graduate in terms of science knowledge.

What has atheism to do with science?

Some might use science to justify their atheism, but it's not part of science to do such justification.

And remember: most science was developed by non-atheists (including evolution and the Big Bang Theory)

Atheism is simply the disbelief in gods. It has nothing to do with science and vice versa. That being said, while most atheists are not scientists, most scientists are atheists.

As with any other group, some do, some don't.  That said, an atheist is probably more likely to accept scientific findings than a religious person, especially if those findings are in conflict with their religious beliefs.  

I've always been interested in science.  I got Scientific American when I was in my teens. If I didn't understand something, I went to the library and researched it as there was no internet then.  Now I frequent hard science sites. 

Albert Einstein did and he was a atheist.

I understand that science is a process.

Very few, just judging from what I've seen.

What do you want, a percentage?  No way to know.

Although atheists tend to understand science better than theists, atheism is not a scientific position.  It's simply not believing in gods.  That's all.