I have a payment agreement with IRS for 2006 back taxes (joint agreement with my husband for our joint back taxes). We are now separated. I filed Head of Household in 2009 and paid those taxes in full. I plan to file that way again for 2010 and, according to my estimates, I may be due a refund. Will the IRS apply that refund to the 2006 back taxes?

Answer: As a condition of your agreement, any refund due you in a future year will be applied against the amount you owe.

• Continue making your installment agreement payments as scheduled because your refund is not considered as a substitute for your regular payment due.
• You may not get all of your refund if you owe certain past-due amounts, such as federal tax, state tax, a student loan, or child support. You can contact Financial Management Service (FMS) toll-free at 800-304-3107.
• The IRS will automatically apply the refund to the taxes owed.

http://www.irs.gov/faqs/faq/0,,id=199566,00.html