The server doesn't grant access to the database: the server reports
To access a database on a PostgreSQL server, you first have to grant primary access to the server for your client (Host Based Authentication). PostgreSQL will check the pg_hba.conf file if a pattern that matches your client address / username / database is present and enabled before any SQL GRANT access control lists are evaluated.
The initial settings in pg_hba.conf are quite restrictive, in order to avoid unwanted security holes caused by unreviewed but mandatory system settings. You'll probably want to add something like
host all all 192.168.0.0/24 md5
This example grants MD5 encrypted password access to all databases to all users on the private network 192.168.0.0/24.
You can use the pg_hba.conf editor that is built into pgAdmin III to edit the pg_hba.conf configuration file. After changing pg_hba.conf, you need to trigger a server configuration reload using pg_ctl or by stopping and restarting the server process.