I was an F1 student in 2011. My compnay will apply for my h1b on 1st April 2012. Under what status should I file my taxes for 2011 year (non resident alien or resident alien). If I file as resident alien can I get American opportunity credit benefit

On F-1 you are nonresident for 5 years. Change in visa in future does not change this. Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents (http://taxipay.blogspot.com/2008/03/us-tax-filing-requirements-for-non.html)