just out of interest, what's your reportingIP in your settings? Should be:
---------- Post added at 01:27 AM ---------- Previous post was at 01:23 AM ----------
I imagine the problem with you trying to join from a PC on the same LAN, is a potential port problem in parallel with your server, it could also be causing a conflict.
Although I haven't looked much into the gamespy side of things, I imagine that the server should be broadcasting to GS on a particular port, but your game PC may be looking to use that same port through the router... see the potential problem?