I'm an NRA(Non resident Alien) on H1 visa and I have spent only 100 days in 2011 in US. My wife too is NRA and with same 100 days spent in 2011 in US. I read somewhere since we are NRA s and under 180 days, we should be filing our taxes separately and as "Single".

1. Does that mean I should not mention in the tax forms that I'm married?
2. If filing separately can one of us file a standard and the other an itemized?
3. If I file a standard deduction, how can I claim for a personal expense I had in those 100 days. I bought a car and to claim that expense, is itemized filing the only option?

Kindly advice.

If you are still in US:
Choice 1: You did not complete SPT in 2011, you can file non-resident tax return.
Choice 2: You can file resident tax return as Married Filing Jointly. You will have to wait for 5 months to file your tax return till you meet the Substantial Presence Test (of 183 days) in 2012. Your U.S. Tax Return: Substantial Presence Test
You will get standard deduction of $11,600 and exemptions ($3,700 each) for both of you. You must both declare your worldwide income for 2009. If you have any foreign income, and on that income you paid taxes in the foreign country, then you can claim foreign tax credit (Form 1116) or you can use Foreign Earned Income Exclusion (Form 2555).
You will complete forms W7 (application for ITIN) for your spouse and attach with your tax return. You can also deduct moving expenses. Use form 3903.

All of what MukatA says is accurate.

If you need professional help doing this, double click on my title above, then scroll down to the signature portion of my profile. There, you will find my email address.