Separation of church and state is a myth. I don't know about your copy of the constitution, but I can't find the words "separation of church and state" anywhere in mine. This country was founded on Judeo-Christian values, and the intention was to keep those values as the foundation of it's governance. The first amendment states that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof..." and was meant to protect the church from the state, and to prevent the state from creating a mandatory national religion; not to remove from the government the founding principals on which the country began. Basically, it was understood that the government would reflect Christian values, but the people are free to practice any religion that butters their toast, or no religion at all.
The country was not founded on Christianity, but even if it were, the 1st Amendment, while not containing the phrase "Separation of Church and State", does guarantee that no government will endorse one religion over the other. The last time I checked, The 10 Commandments are rules from Judaism and Christianity, they're not from the Muslims, Buddhists, etc.. so unless the state is willing to display monuments, writings, etc from ALL religions, they shouldn't display any at all if they want to obey the 1st Amendment. Just because you personally agree with the state's decision, doesn't mean it's not a violation of the Constitution.