2 Citizenships: How to file and pay US taxes living outside the US?

I'm a citizen of 2 countries, USA and Bulgaria. As far as I know, I have to file US taxes even if I don't work in the US.
My estimated income for 2009 in Bulgaria should be around $6,000 per year. This year I spend more than 10 months in Europe.
- Should I file US taxes?
- Should I pay any $$$ to IRS?
- How can I pay taxes to IRS from Bulgaria? Can I use my debit or credit cards and pay online? Or, should I go to US Embassy with form 1040 and personal check?

-If somebody knows a lot about this question, could you please explain me what form should I fill out from IRS site and how? I'll get $0.00 dollars of the US income.

Only serious answers, please.
Thank you.

If you are a U.S. citizen, then you report all of your income, from anywhere in the world to the IRS, and must pay the same tax to the U.S. as you would be required to pay if you were in the U.S. and the income was from the U.S., except that the amount of tax might be reduced by certain credits related to taxes paid to other countries.

However, if your total income for the year is only $6000 and it is not from self-employment, premature IRA distributions, or certain other unusually things, then the U.S. tax will probably be zero anyway. You may still be required to file, but if the U.S. tax is zero, then you do not have to pay.

If you do have to pay, then you can send your check, drawn on a U.S. bank and payable in U.S. dollars to the IRS by mail from almost anywhere in the world. You do not have to go to the embassy and you should not pay online with a debit or credit card. (There is a large convenience fee if you pay with a debit or credit card.) You just need to go to the post office.

Form 1040 is definitely an option. Form 1040A or Form 1040EZ may or may not also be options, and may take less time to complete.

If you are an adult and your worldwide income is less than $9350, you don't have to file unless the income is from self-employment.