I worked in the US for 10 months in 2007 with work visa. Now I have left US and went back to my home country.
1. Do I need to file a tax return?
2. Federal tax, state tax, Social Security and Medicare tax were withheld from my paycheck. Can I claim anything back?
3. Do I have personal tax credit amount to (single: $3400+$5350)? On my calculation deducting this credit amount, it seems the withheld amount is less than my total taxable amount by roughly 400. What do I need to do now?
4. I've lots of other things to worry now. If I don't do anything, will I get in trouble?

Thanks in advance.

1. Yes, you must file the tax return.
2. No, on work visa your income is subject to Social security and Medicare taxes.
3. May be NO. You may need to file Dual status return or nonresident return and you will get only the personal exemption of $3,400.
4. Yes, you must file return. If you have a tax due, you will also pay interest and penalty. It will keep on multiplying. Also you may not get any visa extension or visa to enter the U.S.
You can easily takes the services of a tax professional and for a small few and get rid of your "worry".

My brother has a similar situation.
May I ask how to determine whether he is dual status or resident? Since he is in US for ~300 days in 2007, is he resident and can claim standard dedection?
Is it too late to file now?

This is a provision in the tax code that receives little attention generally and NO MENTION AT ALL in IRS Pub 519: if you spend even ONE day as a non-resident alien, you CANNOT file as a resident alien if you are single.

That is the reason he is dual-status.

My brother has a similar situation.
May I ask how to determine whether he is dual status or resident? Since he is in US for ~300 days in 2007, is he resident and can claim standard dedection?
Is it too late to file now?

It depends upon his citizenship, date of entry in the U.S. if married or not.
He must file his tax return. If he owes taxes he will pay with interest and penalty.