undefined variable?

[Liquid Fire]

ok here is the code in question

$_SITE_CONFIG["admin_password"] = "v4ndr34d";

function CheckAdminStatus($status)
{
if($status == $_SITE_CONFIG["admin_password"])
{
return true;
}
else
{
return false;
}
}

I am getting error:

Notice: Undefined variable: _SITE_CONFIG in C:\WebRoot\root\includes\functions.php on line 13

Why would i get this when it is clearly define in the beginning of the code.

[genericnumber1]

variable scope

http://www.php.net/manual/en/language.variables.scope.php