Some of the earlier nikons are not as tolerant to the higher ISO settings. But to help with low light shooting a faster lens F2.8 will allow more light in. Using a good TTL flash shoe mount for extra light will also help. If you raise the ISO the flash will only deliver the amount of flash needed to the natural light. Slower shutter speeds may be required which may require you to use a tri-pod to prevent camrea shake and picture blur. Low lite shooting can be very rewarding you just need to be prepared the answer is definitly raising the ISO but you need to get as much light to the sensor as you can so you need to decide flash, faster lens, tri-pod, or combination of all if conditions warrant. A good example wood be a wedding where the minister says no flash allowed. You would want your fastest lens and would want to raise the ISO to get the camera speed to a good hand holding speed with the lens wide open (all depends on how much light in church, best to take meter reading if you can), and when posiable shoot in raw to give you most data to work with.
Fotojo