Don't feel bad; I had the same questions the first time I made pasta after starting FitDay. When I made the pasta for myself, I could just weigh out 2 oz. dry on a food scale and cook only that much. However, when the whole family eats it, it's a little more tricky. You could estimate and if you cook, say, 8 oz. altogether, eat a quarter of it, and that would be equivalent to your 2 oz. dry. Alternatively, though it probably varies depending on the kind of pasta, 2 oz. dry is about a cup cooked. That would be your serving size for the info on the package.
There's a chart on this link for different types of pasta...lots of other info, too, but click on the question "How much cooked pasta..." and it jumps you down: http://www.ilovepasta.org/faqs.html#Q10
Hope that helps!