Unfortunately, in the U.S. a spouse can not be forced to file jointly, unless this is ordered by the court as part of a divorce settlment and order.
I see you are using the phrase "I ....lose a lot of money". Why not approach her with "We lose money". She may file jointly if she understands she is getting half the refund.
The botXXXXX XXXXXne, she has to agree to filing jointly. The only way to compel her is for the divorce court to make this a condition of a divorce settlement.
So now for tax year 2009 - can I change my marital status to "married" using form W-4?
The reason I am asking this is - I am guessing that when I file my tax return for 2009 in March 2010, it is going to ask me for filing status. If I say "married" then, is it going to ask me for the ITIN or wife's SSN then? I will still not have iti - will that create problems for me?
The W-4 does not change your filing status., The W-4 determines what the withholding rate is from your salary and wages. The employers uses the information on the W-4 to determine how much to withhold from salary.
If you do not have an employer then you will not be completing a W-4.
Your actual filing status is determined by your status at the end of the year, which you declair when you complete the return.
If you are married, and not yet divorced, your choices at the end of the year are:
1. Married seperate
2. Married joint.
3. Head of household , but ONLY IF, you have lived seperate and apart for the last six months of the year, AND ALSO that you have a qualifying child living with you. (or live seperate and apart by written or legal seperation agreement AND have a qualifying child living with you).
If you have been divorced at the end of the year, your only choices for a filing status are:
2. head of household if you have a qualifying child living with you.,
To file a U.S. tax return in any status, you AND your spouse has to have a SSN or ITIN number. If there is no ITIN number, then the person has to apply for one. The application can be turned in along with the tax return.