java image swap

[SUNBEDKID]

Could anyone tell me how to change the text that is associated to an image as I am totally stuck?

		function renderListingsMainImageJava($listingID)
	{
		// shows the main image

	global $conn, $lang, $config, $style;
	// grab the images
	$listingID = make_db_extra_safe($listingID);
	$sql = "SELECT ID, caption, description, file_name FROM " . $config['table_prefix'] . "listingsImages WHERE (listing_id = $listingID) ORDER BY rank LIMIT 0,1";
	$recordSet = $conn->Execute($sql);
	if ($recordSet === false)
	{
		log_error($sql);
	}

	$num_images = $recordSet->RecordCount();
	if ($num_images > 0)
	{
		while (!$recordSet->EOF)
		{
			$file_name = make_db_unsafe ($recordSet->fields['file_name']);
			$caption = make_db_unsafe ($recordSet->fields['caption']);
			$description = make_db_unsafe ($recordSet->fields['description']);
			echo "<center><img src=\"$config[listings_view_images_path]/$file_name\" width=\"440\" name=\"main\"></center>";

	if ($description == "")
	{
	$description = 'Listing #'.$file_name.'';
	}
			echo "<b>$description</b><br><br>";
		$recordSet->MoveNext();
		} // end while
	} // end if ($num_images > 0)
} // end function renderListingsMainImageJava

	function renderListingsImagesJava($listingID)

This is the function:

echo "<SCRIPT Language=\"JAVASCRIPT\"> function imgchange(name){if(document.images){document.main.src = \"$config[listings_view_images_path]/\" + name;  } else { document.main.src = \"images/nophoto.gif\"; }}</SCRIPT>";
				

Any help please