I entered the US on te 30th of Dec 2004, during the year 2007 from the 1st of Jan to the 1st of Oct I was on OPT and my employeer deducted SSN and Medicare taxes and then I was converted to H1 on the 1st of Oct'07. Will I be able to get back the SSN and Medcare I paid for during my OPT period (Jan-Oct) if "Yes",please let me know how? and if "No" please let me know why?. I would deeply appreciate your reply. Thank you in advance. Let me know if I need to be more specific.

Yes, you CAN get the Social Security and Medicare taxes back that was improperly withheld during your OPT period.

First, you must request that the employer refund these taxes. When they refused (which they will because the tax year has been closed), get the refusal in writing, preferably on company letterhead.

You then submit Form 843 with the refusal letter and other support documents as specified on Page 49 of IRS Pub 519.

It will take about two months, but, eventually, you will get your money IF the IRS agrees with the request. Make note of that: the refund is NOT GUARANTEED. The IRS can and has refused to grant the refund, often for non-valid reasons. The refusal CAN be appealed, often successfully, but the costs make such an appeal problematic.