"relation does not exist", ERROR 42P01

Hi . . I've installed PostgreSQL 8.0, PgAdminIII and the Npgsql .NET data provider.

I've created a user, a database owned by that user, and set the database to accept connections.  

I can connect to the db server, and run a query like "SELECT VERSION()", but when I try to "SELECT COUNT(*)" from any table in the database, I get the error "relation TABLE_NAME does not exist".

Obviously, the connection to the server is fine, but for some reason the connection to the database isn't working.  I've never used PostgreSQL before this (mainly MySQL), so it could definitely be something simple I've overlooked.

Thanks, everyone :)

MK