Pasta cooked "al dente" is a reference to pasta "properly cooked" in the Italian manner. Pasta cooked this way has less impact on blood glucose than pasta cooked in the usual American way.
The term "al dente" literally means "to the tooth," and can be best translated as "chewy." It is a pasta that is boiled just to the point of being cooked through, and remains firm. In the U.S., pasta is rarely served this way except in high-end restaurants, as restauranteurs find that Americans prefer their pasta to be cooked longer. This is unfortunate, because the length of time pasta is cooked can have quite substantially different effects on blood glucose -- even a minute past al dente will make a difference, and the softer the pasta, the higher the glycemic index.
The trick to cooking pasta al dente is start checking about a minute before the minimum time on the package, and then keep checking until the moment there is no white core to the pasta -- then it is cooked through. In other words, "firm" does not mean "undercooked" or "hard."
More on How to Cook Pasta by About.com's Guide to Italian Food.
Leroux, MarcusFoster-Powell, Kaye, Holt, Susanna and Brand-Miller, Janette. "International table of glycemic index and glycemic load values: 2002." American Journal of Clinical Nutrition. Vol. 76, No. 1, 5-56, (2002).