this might be able to help you: http://travel.state.gov/travel/cis_pa_tw/cis/cis_1753.html
A U.S. citizen may acquire foreign citizenship by marriage, or a person naturalized as a U.S. citizen may not lose the citizenship of the country of birth.U.S. law does not mention dual nationality or require a person to choose one citizenship or another. Also, a person who is automatically granted another citizenship does not risk losing U.S. citizenship.
<b>However, a person who acquires a foreign citizenship by applying for it may lose U.S. citizenship. </b>In order to lose U.S. citizenship, the law requires that the person must apply for the foreign citizenship voluntarily, by free choice, and with the intention to give up U.S. citizenship.