Tax Credit is a bust, or is it ?

I did my Taxes on TT and was totally outraged to see my credit for buying a 2006 Prius go to ZERO , but then I started reading, for two days I have read tax info, publications from the IRS, etc.

So I started over and instead of filing Married Jointly, I did them seperately and it works....
My only problem is that I can't get a straight answer of Who gets to claim the mortgage interest deduction if we file seperatly.
Most I have read says it can be split, or we can decide who gets to claim it.
I am putting the Prius Credit on my Wife's taxes, she made less(and both names are on the Prius) , and I want my wife to use the interest on the mortgage, it comes out betterthat way it seems.
I am putting the Child Credit on mine (IRS seems to say that the higher income needs to use the Child credit).


I know we both have to itemize if one of us itemizes, but Who would list our State tax refund as income? Do we split that in half as income, since we itemozed last year and it is taxable? I would think we should split that between us.
My main problem is who gets the mortgage interest deduction and if it matters!