Could a pacemaker keep an individuals heart beating after a cardiac arrest. If the answer to the above question is yes, then how long would it continue to assist the heart in beating and would it help to prevent brain damage until medical help arrives.

Generally no. In most circumstances the term cardiac arrest refers to a rhythm problem called ventricular fibrillation. Eventually there is no electrical activity at all and even a pacemaker cannot stimulate the heart.
Yes.. Yes. A pacemaker is placed in the heart to prevent the heart from beating too slow. As an example a pacemaker may be set to ensure the heart beats 70 times a minute. If your intrinsic heart beats slower than 70, or if your heart stops beating (as in a cardiac arrest), then the pacemaker will send an electrical impulse to the heart to keep beating at 70 beats per minute. To avoid brain damage, the person must also be breathing normally. If the person is not breathing normally (10-20 breaths per minute), call 911 and initate cpr.