JDBC connection refused

I have Postgresql set up on RedHat 6.1, and I can access it with jdbc or
pgaccess locally, and with pgaccess from another linux box on the same
local net. However, I can't get a connection with jdbc across the net.
The relevant code is

public static void main (String[] args) {
try {
Class.forName("postgresql.Driver");
Connection con =
DriverManager.getConnection("jdbc:postgresql://birch/auction",
"collins", "");
// Do something useful here
Statement stmt = con.createStatement();
....

and the error message is

Connection refused. Check that the hostname and port is correct, and
that the postmaster is running with the -i flag, which enables TCP/IP
networking.
at postgresql.Connection.openConnection(Connection.java, Compiled Code)

at postgresql.Driver.connect(Driver.java, Compiled Code)
at java.sql.DriverManager.getConnection(DriverManager.java, Compiled
Code)
....

Here's what I've checked:
- postmaster is indeed being run with the -i flag. I think neither the
local jdbc or the remote pgaccess would work otherwise. Here's the line
from rc.d/init.d/postgres:
su -l postgres -c '/usr/bin/postmaster -i -S -D/var/lib/pgsql'
- I've used every name I can think of, including the ip address, in the
URL above. I've used the port and I've not used the port.
- I've used netstat to check that postmaster is indeed listening on
5432

I'm stumped. Thanks in advance for any assistance.

John Collins
University of Minnesota