Hi,

I came to US on F1 in August 2011. I started working from Jan 12, 2011 on OPT visa. My H1B was filed in April 2011 and became effective from October 01, 2011. I my employers withheld social security tax and medicare tax along with Federal tax and state taxes. I want to know if I can get any refund for my OPT period on any of the taxes I paid. Also what are the forms I need to feel and what additional documents I need to submit with those forms.

From Jan 2012 to Sept 30, 2012 your employer should not have withheld social security and medicare taxes. On your income during H1-B, you must pay FICA taxes.
For OPT period, ask your employer to refund you the FICA taxes as you are nonresident during OPT.