The new SAT allows the use of approved calculators, and the College Board (the people who sponsor the exam) recommends that each test taker take a calculator to the test. Even though no question will require the use of a calculatorthat is, each question can be answered without a calculatorin some instances, using a calculator will save you valuable time.
You should

Bring your own calculator, because you can't borrow one during the exam.

Bring a calculator even if you don't think you'll use it.

Make sure that you are familiar with how your calculator works.

Make sure that your calculator has new, fresh batteries and is in good working order.

Practice using your calculator on some of the problems to see when and where it will be helpful.

Check for a shortcut to any problem that seems to involve much computation. But use your calculator if it will be time effective. If there appears to be too much computation or the problem seems impossible without the calculator, you're probably doing something wrong.

Before doing an operation, check the number that you keyed on the display to make sure that you keyed in the right number. You may want to check each number as you key it in.
Be careful that you

Don't rush out and buy a sophisticated calculator for the test.

Don't bring a calculator that you're unfamiliar with.

Don't bring a pocket organizer, handheld minicomputer, laptop computer, or calculator with a typewritertype keypad or paper tape.

Don't bring a calculator that requires an outlet or any other external power source.

Don't bring a calculator that makes noise.

Don't try to share a calculator.

Don't try to use a calculator on every problem.

Don't become dependent on your calculator.
Following is the Calculator Policy for new SAT as given by the College Board:
"The following are not permitted:

Powerbooks and portable/handheld computers

Electronic writing pads or peninput/stylusdriven devices (e.g., Palm, PDAs, Casio ClassPad 300)

Pocket organizers

Models with QWERTY (i.e., typewriter) keyboards (e.g., TI92 Plus, Voyage 200)

Models with paper tapes

Models that make noise or 'talk'

Models that require an electrical outlet

Cell phone calculators"
Take advantage your calculator during the test. As you approach a problem, first focus on how to solve that problem and then decide whether the calculator will be helpful. Remember, a calculator can save you time on some problems, but also remember that each problem can be solved without a calculator. Also remember that a calculator will not solve a problem for you; you must understand the problem first.