Ok, how come I can't bind to INADDR_LOOPBACK under MacOSX (10.3.4)? If I try to connect to 127.0.0.1 to something listening to INADDR_ANY, the two sockets are IPv6, so I suspect that's part of it, but lo0 is enabled for IPv4 at 127.0.0.1.
This has always worked for me on other Unix systems...