No, the law is about driving with a certain level of blood alcohol in your system. You can indeed drink and drive if your blood alcohol is not above a certain level. In most states, that is 0.10 percent; in Vermont and a number of other states, it's 0.08 percent.
http://www.insure.com/auto/baccalc.html has a calculator that will tell you how many drinks you can consume within a particular time frame and what your blood alcohol level will generally be. Heavier people can drink more without their blood alcohol levels rising as quickly. For example, I could have five glasses of wine during a two-hour dinner, and my blood alcohol level would still be half the legal limit in Vermont and elsewhere. But I also know that five glasses of wine, while it wouldn't impair me, it would make me less sharp and responsive, so clearly at the legal limit, I would be quite drunk indeed....
.:. Craig