I found this great application that will scan all your ports and tell you which ones are open, being used or are closed. It may be useful for port forwarding. But the new patch mostly will take care of that. Anyway, it might be useful for other things as well. A firewall will block most ports and hence you will not have many ports that are open. But you can see if a port that you want open is closed. this won't work for routers that do not have a loopback feature enabled. Otherwise it*should* work fine.
Cheers
