Enable Mac OS X 10.5 syslogd to receive log from router

To enable your Leopard system to receive network syslog submissions edit:
/System/Library/LaunchDaemons/com.apple.syslogd.plist

Uncomment the paragraph commented: "Un-comment the following lines to enable the network syslog protocol listener".

Then execute the following commands:
sudo launchctl unload /System/Library/LaunchDaemons/com.apple.syslogd.plist
sudo launchctl load /System/Library/LaunchDaemons/com.apple.syslogd.plist

That should allow your external device to dump it’s log into the system log.
If you have firewall enabled make sure to allow the traffic (UDP 514) from router.