iptables redirect

Hi

I need your help.

This is my problem, i have a VPN connection between two computers a and b. A is connection to b(vpn server) i want to redirect some ports to a and i want a to give internet access to those port. So far i redirected the port 22 from b to a but i can't make a sent the port out to internet.

I will apreciate your help.

Thank you.