I am H1B visa since Oct 2004. My Husband was on H4 during the year 2006 when he arrived in The US and he changed his status to F1 student visa sometime around March 2007.

He did not have any income during 2007 year and I filed my taxe status as "married filing jointly"

My husband started his internship in May 2008 till present. Now for the 2008 tax return can we file separately. Can he file 1040NR, 1040EZ and 8843 because he will get a bigger refund if files as a non resident status.

Can I file my tax return as "married filing seperately" or do we have to file jointly.

Even for 2008 your husband is resident and can not file nonresident tax return. His income is subject to FICA taxes.