You need to say math.sqrt when you use it. Or, do from math import sqrt.
Hmm, I just read your question more thoroughly.... How are you importing math? I just tried import math and then math.sqrt which worked perfectly. Are you doing something like import math as m? If so, then you have to prefix the function with m (or whatever name you used after as).
pow is working because there are two versions: an always available version in __builtin__, and another version in math.