What do Error 1, Error 2, and Error 3 mean?

From Joomla! Documentation

Error 1 = FATAL ERROR: MySQL not supported...

You need to compile MySQL support into PHP or the MySQL server is down.

Error 2 = FATAL ERROR: Connection to database ...

Joomla! cannot talk to the database, most likly you have a typo in the username or password settings in configuration.php, or you are trying to access a database table with the wrong table prefix.

Error 3 = FATAL ERROR: Database not found...

The database cannot be found. Check the database settings in configuration.php

The MySQL variables in configuration.php (found in Joomla!'s root directory) can be modified to correct these problems.

For Joomla! 1.0.xx

$mosConfig_host = 'localhost';
$mosConfig_user = 'accountname__username';
$mosConfig_password = 'userpassword';
$mosConfig_db = 'accountname_dbName';
$mosConfig_dbprefix = 'jos_';

Modifying the $mosConfig_host to an IP Address of a remote host works for hosts that have separate MySQL servers from the client hosting servers.