I just had this done last week. So you'll get a police clearance letter from your home city in the US... Mine cost $10. It said something like this:

Mr._____________ of 123 Main St. Sacramento, CA, Passport#xxxxxxxxx has no record of arrests or convictions.

That's about it. There were no fingerprints, FBI/DOJ clearances etc. Easy. It might be more difficult if you're out of the country... I did have to show my ID to the cops to get the letter.

When I got to Qatar, I went to the US embassy. (Be sure to look up their hours and give yourself a lot of time to get through securty.) Take the letter and your passport and $30. You'll have to write on a blank paper something like, "I swear the attached letter is true." They they'll ask you if you're the person in the letter. Say yes. Then they'll ask if you swear what you just wrote is true. Say yes. They stamp the letter and charge you the $30. Take the letter to your HR dept. and you're done.