Moms, I have a quick question about going back to work and taxes?

I am going back to work only part time tho. I will be about 60-70 dollars a weekend. It will be enough to pay for her diapers,formula and everything that she may need for that month. However I became a stay at home mom and on our 2009 taxes we filed jointly. Now that I will be working,would it be better to file together or sepertly? Will it affect much of our taxes? Thanks for the advice.