Siran,
To label numbers divisible by 100, use the modulo operator. In the label expression advanced box, set the parser to Python. Then use a function like below:
def FindLabel(somefield):
if somefield % 100 == 0: return somefield
if you want to label with a different field based on somefield:
def FindLabel(somefield, anotherfield):
if somefield % 100 == 0: return anotherfield