Help with ipfw please

[Tiago]

Im trying to add a basic rule in my ipfw.
My server has 2 network address, one for external access (x.x.x.x) and other
for the local network(y.y.y.y).
The mysql is binded to the local network, but I would like to allow my home
computer (z.z.z.z) to connect to the mysql by the external ip.
so basicaly im trying to do is: if request comes from z.z.z.z to
y.y.y.y:3306 redirect to x.x.x.x:3306
I tryed some configuration but I ended locked outside the machine...