I'm thinking about going to law school after I graduate college. Will that help my chances at being a JAG?

It's the only way of becoming a JAG. You have to be a lawyer first, then enter the service as a JAG.

See this thread as well:
http://military-forums.net/eve/forums/a/tpc/f/7461073/m/9671047222

I am planning on becoming a JAG after reading this from the Official JAG website:

11. WHAT ARE THE RANK AND PAY OF A NEW OFFICER IN THE NAVY JAG
Attorneys entering the Navy JAG Corps via the Direct Appointment (DA) Program are appointed as lieutenants junior grade, pay grade O-2 (See paragraph #23 below for description of DA Program.) They may expect promotion to lieutenant, paygrade O-3, approximately one year after they begin extended active duty. Individuals who enter through the JAG Corps Student Program (SP) will be commissioned as ensigns. (See paragraph #23 below for description of SP Program.). If they join in law school and participate in the JAG Corps Student Program for more than two years, they will be eligible for promotion to lieutenant junior grade while still in school. In any event, they will be promoted to lieutenant junior grade at the time they accept superseding appointments in the Navy JAG Corps to designator 2505, upon commencement of studies at the Naval Justice School, at which time they leave the SP rolls. Participants in the Student Program are eligible for superseding appointment to lieutenant junior grade when they commence extended active duty after having passed their bar examination. They may expect to be promoted to lieutenant approximately one year after their graduation from law school.
Active duty judge advocate pay starts at between $53,000 and $60,000 per year as a LTJG (0-2), depending on when the officer accepts a commission and where they are stationed (This salary uses the January 2004 pay scale and includes non-taxable allowances). Within one year or less and promotion to LT (0-3) an officer can expect to earn between $60,000 and $77,000 per year - through a combination of pay increases due to promotion to lieutenant and longevity increases. Current information on base pay and allowances, such as the Basic Allowance for Housing (BAH) and Basic Allowance for Subsistence (BAS), is available at www.dfas.mil. BAH allowances vary according to the cost of living in the relevant geographic area.

JAG Careers FAQ

Hmm, perhaps you need to look into the term by Direct Appointment first. Regardless, good luck with your endeavor.