@Thomas,
However rosborne's question relates to the CNN story, it was impolite of me not to answer it. Here's my answer:
Yes, I think Atheist messages should get equal exposure in public buildings, including the Legislative Building in Washington. The state cannot discriminate on the basis of faith, so it cannot grant Christians exposure in government buildings and deny it to others.
The state can, however, discriminate between signs on a basis other than religion. And if the sign at issue here said something like "Why believe in God?", I think the government can still ban it, on the grounds that Christmas is a celebration, and that sign constitutes party-pooping, atheist or not.
With this distinction, Christians can put up signs celebrating Christmas, and atheists can put up signs celebrating Newton Day. But Christian signs can't say, "why did the Jews kill Jesus?", Jewish signs can't say, "why did Christians kill six million Jews in the Holocaust?", and Atheist signs can't quote Richard Dawkins stating that "the god of the Bible is the most unpleasant character in all fiction."
Sound fair?