It's been a while since I did FAFSA for undergrad, but it's not a loan. It's a form that determines your financial need, which is used by schools and the goverment to qualify you for the federal loans and any aid from the school. From what I've seen it doesn't look like many postbac programs give any kind of aid/grants ("free money"), and most people take out the federal and private loans to subsidize the cost.
I do have a question for other people regarding the FAFSA. I'm still waiting for decisions from some programs, but Drexel encourages applicants to fill out the FAFSA before a decision is made, otherwise you may not qualify for federal loans for the first semester. However, I'm applying to both "masters" (Drexel, UMDNJ) and "undergraduate" level programs (UCONN, UPenn). Do I just pick "graduate" or "undergraduate" for level of study on the FAFSA, and change it later, if I end up getting into a different program? I believe the level of loans you can qualify for is different depending on if you are doing undergrad or grad level study, so I don't see how I can fill it out before getting an admissions decision. Is anyone else in a similar situation?