My mother is filing married separately, she has some income and my father none. Both lived with me and I cover all household expenses. Can I claim my father as a dependent?

Yes, if you provided more than half of the support of your father and he did not earn more than $3650 in 2009. You are head of household if you are not married. Your U.S. Tax Return: Filing Status: Head of Household (http://taxipay.blogspot.com/2008/05/head-of-household.html)