How Do I Toggle Quoted Identifiers?

I'm on PHP 4.2.2 and RedHat 9 with PGSQL. I want to turn quoted
identifiers off with my SQL queries. What SQL statement or .CONF
setting do I need to change so that I can turn quoted identifiers off?

Quoted identifiers, as I understand them, are where you must put
double quotes around any table or column name in order to preserve its
case, or in order to preserve an internal space it may have in the
identifier name.

I was looking for something like:
SET QUOTED_IDENTIFIERS = OFF;
SELECT Username FROM Logins;

For that matter, how do I turn case-sensitivity off?