Easiest method might be in the includes/languages/english.php. All the defines are around lines 484 -- 491.
Code:
if ($_SESSION['customer_id'] > 0) {
define('TABLE_HEADING_FEATURED_PRODUCTS','Featured Products');
define('TABLE_HEADING_NEW_PRODUCTS', 'New Products For %s');
define('TABLE_HEADING_UPCOMING_PRODUCTS', 'Upcoming Products');
define('TABLE_HEADING_DATE_EXPECTED', 'Date Expected');
define('TABLE_HEADING_SPECIALS_INDEX', 'Monthly Specials For %s');
} else {
define('TABLE_HEADING_FEATURED_PRODUCTS','Log in to See Prices For Featured Products');
define('TABLE_HEADING_NEW_PRODUCTS', 'Log in to See Prices For New Products For %s');
define('TABLE_HEADING_UPCOMING_PRODUCTS', 'Log in to See Prices For Upcoming Products');
define('TABLE_HEADING_DATE_EXPECTED', 'Log in to See Prices For Date Expected');
define('TABLE_HEADING_SPECIALS_INDEX', 'Log in to See Prices For Monthly Specials For %s');
}
Adjust the text to suit your taste.