I have 2 w2 forms from same employer: 1 for CA and other for MI. Only the 16/17/18 fileds differ rest of the fileds remain same. Should I file 1 1040 and different state returns i.e for CA and MI

If you worked or lived in CA and MI, you will file return for both the states. Your U.S. Tax Return: Working or Living in Two or More states (http://taxipay.blogspot.com/2008/06/working-in-two-or-more-states.html)