I was of the impression Netgear supported UPnP which should mean no need for manual port forwarding. Depends on your model & firmware version I guess. If you manually port forward for one computer for LW, then you must do a separate port forward for the other computer using a different port if you want to use LW on both (eg: port 6346 for one & port 49123 for the other). Also, did you make sure you set up a static ip for OSX? Here's a couple of links that explain how to do it http://www.blizzard.com/support/wow/?id=aww01180p & also http://www.sonic.net/support/ss/mac/osx_staticip/ (ignore the domain servers in this example!)

So if you didn't set up a static ip 1st, then you'll need to do the manual port forwarding from scratch & delete your previous effort.

Alternatively, check out your UPnP options for your Netgear. Connection problems? Check here first! (click on link)

Remember also that if you're using LW on both, you'll be sharing bandwidth. So one LW on one computer may take more bandwidth than the other at times. lol