Airport is as much of a network as Ethernet is. Port 139 is the normal port for SMB connections. (At the terminal, try "grep 139 /etc/services".) What you want to do is figure out where your Powerbook was connecting to a Windows file or printer server on network 192.168.0.0 or 192.168.131.0. Are either of those the network address for your Airport network? You can see this in your Network settings.
Login Items is the first place to look for an alias that might trigger an automated mount, but another application (other than the Finder) could be looking for a file server, too (as another posted mentioned). You could try to grep for "192.168.131.65" in all the files in your Preferences folder, except if you have 10.4 they might all be binary now and you'd have to convert them to xml text first, using plutil (again in Terminal).