I think an MA can help, but if you are considering finishing an MA in 1 year and reapplying for Fall 2009 for the PhD, I don't think it will. You have to remember the bonuses of working on a MA include getting to know faculty and them knowing you rather well, proving with your GPA you can do graduate work, and proving with your thesis you can do primary research and have a strong grasp of your field (both of which your major advisor can atest to in their LOR).
If you are applying again by Dec 1, you wont have much time for faculty to assess your abilities, you won't have any graduate class grades on your transcripts, and you wont have much of your thesis written for your advisor to say you will be finished in time to start a PhD.
If you are going to do a 2-year MA, then I think it would give you these added benefits when you get to Fall 2010 apps...but I'm not on adcoms.