Is your OSX firewall enabled or disabled? I only occasionally run mine. If it's enabled then make sure it's been set up to allow LW full access; see OSX Firewall settings for Tiger

I see you have the infamous Linksys WRT54G. Don't get me wrong, Linksys make very good devices, but the models with 54 & especially the WRT54G are almost lemons; this model has a firmware problem. It doesn't run reliably in UPnP mode & is best port forwarded. The other option is to use a crack to fix the firmware. See Linksys WRT54G - Fixed my problem, Followed these steps and it works! for a solution! But you do it at your own risk.

For port forwarding the WRT54G, there's 3 steps: 1. 1st you need to set up a static ip. 2. Then forward a port. 3. Then set LW settings for port forward mode.

1. Static ip for OSX, see these links to get an idea: BTW Domain box can be left empty, it's not important. If used should relate to your local ISP. Sample (i): Static ip for OSX (1), ____ (ii) Static ip for OSX (2), ____ (iii) Setting up static ip (linksys),
(iv) See step 3 in this link about setting up static ip on OSX - Linksys support.

2. Port forwarding step: Some Linksys port forwarding instructions. Those are examples. You only need to forward port 6346 for both UDP & TCP.

3. Within LW: Manual port forward instructions & sample image