If you think the American government practices a double standard in dealings with undemocratic governments, that's a situation you can't do much about if you're not an American. What you can do much about is closely examine your own government's dealings with undemocratic governments; when you find instances of a double standard, lodge protest with your government. In this way, many hands make light work of ending oppressive governments.
To say that America's dealings with oppressive governments do not always meet our standard overlooks that with each US administration the standard has been set progressively higher. During his inaugural address today President Bush set the bar so high that even a Texan might ask whether he's committed America to a quixotic path.
Do not think that Americans don't ask such questions for we are a people characterized as much by practicality as by love of freedom. To be an American is to first ask, "Is it do-able?"
The answer is that it's not possible for America alone to run tyrannical governments off this planet. What Americans can do is set a standard for their own government's interactions with oppressive regimes and struggle to insure that their government meets the standard.
As to America's right to exhort other governments to do the same--the United States is a young country but its government represents history's oldest written constitution. The United States is the world's oldest republic and democracy. So if the right to lecture is conferred by age, the American government has the right to lecture on freedom.