Python, 112 chars
The numbers should be the 1st and 2nd argument: python this.py 4 3
** operator not used.
* used. It's quite trivial to implement, exactly like **, but costs more than 5 chars.
import sys p=lambda y:y and x*p(y-1)or 1 t=lambda y:y>1 and p(t(y-1))or x x,y=map(long,sys.argv[1:]) print t(y)