For FY 2009 whay will be the benefit of Married Joint filing if spouse is having either SSN or ITIN ? Can someone let me know in terms of numbers too that ll be helpful , thanks in advance.

In most cases, it is better to file as MFJ. On the joint return your standard deduction is $11,400 and you get two exemptions.

If you file MFS, you will not get many credits and deductions including EIC.

On the joint return the liabilities are joint. If one spouse owes tax, both spouses are equally responsible.You may file Form 8379 with joint return.

This is from IRS publication 17: Your Federal Income Tax.
Tip. If you and your spouse each have income, you may want to figure your tax both on a joint return and on separate returns (using the filing status of married filing separately). Choose the method that gives the two of you the lower combined tax. Your U.S. Tax Return: Filing Status for Married (http://taxipay.blogspot.com/2008/02/filing-status-for-married.html)