| I don't think that you would be subject to any garnishment due to your spouse's prior obligation despite living in a community property state in this instance as you have separated. I really don't think that the IRS would really be after you for any child support that is owed to you!
You will definitely get a favorable tax treatment by filing as Head of Household, not only will you be entitled to a higher standard deduction $7,850 for your 2008 tax return, but you will also get the benefit of being able to claim the child tax credit and possibly even qualify for the earned income tax credit! | 
