Yeah, troubleshooting internal networks can be a real pain, and will likely continue. With so many devices each trying to make routes to the internet, there are bound to be collisions. I've not used and Airport (or 10.5), so look to google or the Airport Help for making the airport only work as a switch.

The principle to get around all the UPnP or other such protocols is to manually set a unique route from each LW to the internet. This means manually setting the Ip in the OSx Network prefs, setting the Port in LW, and finally using that info to set the router's port forwarding prefs. Quite a pain.

btw, the link LOTR send you will show blank settings until you fill in the box that says "Do not skip this step"

Also, if the browser connections die, that may mean too many incompletes are trying to connect.