Taxes

I'd either get Turbo Tax or hire someone.  It's the state returns that are going to kill you, especially Mass.

I am not a tax attorney, or even a CPA but first off, it depends on what your marital status was on December 31, 2008.  Also, even if you were still marrid on that date, it depends on how long you had been separated from you spouse.  If you had been separated for more than 6 months, then you can file as Head of Household or even Single.

Since you worked in several states, you will still file one Federal return but you'll have to file state returns for each of the states where you earned income.  As far as the car, it will only matter if Michigan requires the payment of ad valoram taxes.  If that is the case, if both of you itemize deductions, you two will have to decide who will take the deduction.  Also, if the vehicle is used for business purposes or if there will be any non-reimbusred employee expenses for use of the vehicle, you two still will have to agree on who will take the deducttion.

Regarding the chidcare, if he pays for chidcare, I think he can still claim the deduction if he can prove that he made the payments, but you can claim her as a dependent.  Also, both of you can claim childcare expenses if both of you paid childcare costs in 2008.