The SAT is broken up into three subjects: math, verbal and writing. There are three math sections, three verbal sections, two grammar sections and an essay (which combine for the 'writing' score), and an unscored experimental section used for future tests. The best score for each subject is 800 with 200 the poorest score on any one subject. A 'perfect' score on the entire test is 2400, the worst possible score is 600.
Each question on the test is worth one raw point regardless of difficulty. A missed question carries a penalty of -1/4 of a point and omitted questions receive a score of zero, neither adding to nor reducing the score. These raw scores are converted to a final score by multiplying the raw score by approximately 10 points.
A student can receive a 'perfect' score on the test today even though she has missed a couple of questions because the test is curved. After all the tests have been marked, the scores are equated to ensure that the May test wasn't 'harder' than the March test was. What this means in practice is that students who score in the middle on a given subject, receive a 500. This is done in part so that college application reviewers have a year in year out standard of comparison. Because of the curve, students may receive an 800 on a subject subscore even though they have missed one or two questions. This is true for each subject, though it seems that the verbal portion of the test generally allows for the most misses.
Hope this helps with working out how it's scored! Leave me a note if you'd like clarification.