I graduated with an undergraduate degree in psychology, and went to law school two years later. I did well, Dean's List, top 10%, but I withdrew after a year.
Keep in mind a couple things. First of all, a law degree does NOT guarantee you a high standard of living. The dirty secret these days, even more so than when I entered law school 10 years ago, is that law firms are laying people off left and right. There is absolutely no guarantee of a job, even if you graduate from a top law school and were on law review. I know some people cobbling together contract work including "document review" work a trained monkey could do. People always equate lawyers with money, and it's often not the case.
Second, law school is about a million times more difficult, academically, than an MSW, so be realistic about your abilities and your ability to stick with something which is, quite frankly, often boring, even if you're generally interested in law.
Third, law school is usually crazy-expensive.
Fourth... law or social work? Seems like a funny question, because they're such completely and utterly different fields. There was actually a girl in my class who has the MSW and had worked as a social worker for awhile, and been honored by state organizations, etc.. She realized, after working with down and out clients, that her passion lay with providing legal help to the same population. But that's different from saying, "I don't like being poor, I want to make money." She's not going to make much money doing the kind of legal work she wants to do.
Think carefully about your TRUE interests... many lawyers hate their jobs and there is a high rate of suicide. Many other lawyers love their jobs. Many social workers love their jobs... many are also burned out and hate their jobs.
Do your research into the job markets in both fields, the realities of admissions, tuition, funding, academic difficulty, etc..
My major advice to you is to wait a few years to decide which graduate program you'd like to enter. You'll know yourself and the world better then.