My brother worked on work Visa in US for 9.5 months in 2007, now that he has left US.

1. By the substanial prescence test, he should be a tax resident. Correct? He has very little or no other world income. Is it better for him to claim as resident, then he have standard dedection?

2. Will he be eligible for Stimulus Payments?

3. Is it too late to file now? He has not done that yet.

Thanks so much for all your help.

Your brother is not resident for tax purpose. He is dual status alien; must file dual status tax return. He will not get resident tax return. Will not get standard deduction.

He must file tax return if he made more than $3,400 in 2007. He will not get stimulus tax rebate.
For information on stimulus tax rebate schedule, the eligibility and how much rebate you will get read: Your U.S. Tax Return: Are You Eligible for 2008 Stimulus Tax Rebate Payment?

Thanks MukatA for your help!

Is the amount for Social Security and Medicare tax detectable when filing federal or state tax return? In another way, if he pays $2000 for SS and $600 for medicare, can he cliam $2600 as tax credit or other detection on any tax return?

Negative.

Neither Medicare nor Social Security tax payments are deductible on either the employee's nor the employer's tax returns.