Welcome to Just Answer. I am here to help you resolve your tax and finance concerns. Please feel free to ask anytime you need extra help.
In any divorce situation I advise filing separate returns regardless of the tax cost. To you it will be a savings, but will cost you almost ex a bit more. The reason I recommend separate returns is that neither of you can then be held responsible for any shortcomings on the others return. It's a safety thing in these situations. However, there are rules as to how you can file. The IRS has a statement about this which I will attach for you.
IRS Tax Tip 2011-09, January 13, 2011
The first step to filing your federal income tax return is to determine which filing status to use. Your filing status is used to determine your filing requirements, standard deduction, eligibility for certain credits and deductions, and your correct tax. There are five filing statuses: Single, Married Filing Jointly, Married Filing Separately, Head of Household and Qualifying Widow(er) with Dependent Child.
Here are eight facts about the five filing status options the IRS wants you to know so that you can choose the best option for your situation.
There's much more information about determining your filing status in IRS Publication 501, Exemptions, Standard Deduction, and Filing Information. Publication 501 is available at http://www.irs.gov or by calling 800-TAX-FORM (800-829-3676). You can also use the Interactive Tax Assistant on the IRS website to determine your filing status. The ITA tool is a tax law resource on the IRS website that takes you through a series of questions and provides you with responses to tax law questions.
Publication 501, Exemptions, Standard Deduction, and Filing Information (PDF 196K)