Are you using LW for Leopard or Win 98? If both, you will probably need to set a different port for each. And different to any other computer. ;)

Did you set a static ip "before" you did the port forward?

The Win98 Box is also running LW and has a static IP, it has no problem w/ LW. The OSX machine is wireless and I have used different ports for listening and for accessing the web 6346 manually from w/i LW. Only 2 computers on network. I could try but am apprehensive of setting Static IP for OSX machine.

I used to have to use different port for osx & windows 2000 using virtual pc. For osx try another between 49152 - 65535 for both connecting & listening through.
I am not sure how it works with both windows & osx, but I'd have thought the router would think of them both as being the same computer & same ip. My knowledge of networking is highly limited in how the numbers are given out, particularly for a single machine.

Are you trying to run them at same time? I do know that routers can get mucked up if two programs try to connect from same computer using same port even at different times & a reboot was necessary.

Is your router set to use UPnP for OSX? If not, then it will be blocked from incoming from whatever port it's set to.