Cannot connect to postgresql

I have just downloaded and installed postgresql and pgadmin3.

In Postgresql I have done no more than create a test database (with no
tables or anything) called testdb.  I can connect to this dataabase as
the user postgres from the command line interface (./psql testdb).  The
postgres user is the user who started the server.

When I try to add a server in pgadmin3 I firstly get the following
warning:

Warning:
Mailcap file /home/peter/.mailcap, line 59: incomplete entry ignored.

which seems a bit odd, since that refers to crossover office's entry for
Word 97 ...

Then I enter the details for the new server (localhost, testdb,
postgres), but pgadmin3 hangs when I click on OK.  I've tried it with
the trusted checkbox both selected and deselected.

netstat -l confirms that the server is listening on port 5432.

If I try to telnet to port 5432 I get "Connection refused" both as my
own user and as the postgres user.

My pg_hba.conf file is just the default file, which says that
connections should be permitted for any local postgresql user.  So I
gather from that that the postgres user should be OK.

I'd look in the logs, but I don't know where to look (or what to look
for ...).

I'd be grateful for any help

Thanks in advance

Peter