Need help with Joomla 1.5.2

[babydol]

Hi I am trying to learn Joomla - a tool for web development using php.My problem is I keep getting warnings such as

Warning: strtotime() [function.strtotime]: It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Pacific/Auckland' for '12.0/no DST' instead in C:\xampp\htdocs\joomla15\libraries\joomla\utilities\date.php on line 56

I tried changing the code

function __construct($date = 'now', $tzOffset = 0)
	{
		if ($date == 'now' || empty($date))
		{
			$this->_date = strtotime(gmdate("M d Y H:i:s", time()));
			return;
		}
                 :
                 : //more code

        }

to

function __construct($date = 'now', $tzOffset = 0)
	{
		if ($date == 'now' || empty($date))
		{
			$this->_date = date_default_timezone_set('Pacific/Fiji');
			return;
		}
                   :
                   :  //more code
          }

Before changing the code, I got the home page as I had designed, together with the warnings but now I get a blank page.I can't even view my home page.Can someone familiar with Joomla help me please...

Thanks