Just spent quite a bit of time searching for this.
On a Xserve (10.6 OS-X server), the com.apple.syslogd.plist lacks the
"commented section" that enables listening on port 514 for syslog
messages coming from routers etc.
Lots of web pages mentioned you simply needed to uncomment it. But on my
system, it wasn't there to be uncommented. (perhaps because I used plist
editor forst and perhaps it zaps comments).
Anyways, just for sake of documenting (in case Google re-eneables
searching of newsgroups)
Un-comment the following lines to enable the network syslog protocol
SockServiceName = syslog
Socktype = dgram
(there are already 2 "Sockets" entries, you don't modify them, you add
the NetworkListener one).
It would be nice if Apple added this in the man page that discusses
changing the plist to enable listening to port 514