How do I proceed filing my 1040X and 5405 to get the first time homebuyer credit?

So when I filed my 2008, my then girlfriend and I were single and hence both filed single. We got married in May 2009 and purchased a house last month. I am filing for the first time homebuyer credit (I have all forms already) and I was wondering if we now have to file jointly as a married couple even though we both filed single in 2008. Do we just combine adjusted incomes, tax paid, etc? Or can I just claim the 8000 under my name and the two of us share the 8000?