You may be confused. The gamma function is unrelated to the function x^y. Perhaps you are thinking of the relationship Gamma(n+1) = n! for nonnegative integers n. Moreover, Gamma(0) is undefined (as is, more generally, Gamma(n) for nonpositive integers n).
(For those who are curious, the gamma function is most easily defined as the Gamma(x) = integral from 0 to infinity of e^(t) * t ^ (x1) dt. Google can pretty easily be convinced to take you to more information about it. But it's pretty much unrelated to the topic at hand.)
