That depends on if it is included in box 1 (regular interest payment) or box 3 (US treasury Interest) on the 1099-INT Form.

If the amount is included in box 1, then just include the interest income as you would id it had come from anybody else such as SmithBarney, Edward Jones, Bank of America, etc...

If the amount is included in box 3, then you start the process to enter the information as you would for ordinary interest income, however...you must check the box that states "My form has info in more than just box 1 (this is uncommon)." This will bring up several other boxes (all numbered to match the 1099-INT). Then you simply enter the income into Box 3 in Turbo Tax. Finally, continue to follow the on-screen prompts about your particular situation.