date problem

Hi all I have a database that holds car rental info DB: carrental_from (datetime field) carrental_to (datetime field) carrental_price (datetime field) [rates are per hour] The values I have are like: 0000-00-00 00:00:00,0000-00-00 07:00:00,10 (all year around 00:00-07:00) 0000-00-00 07:00:00,0000-00-00 00:00:00,20 (all year around 07:00-00:00) 2005-12-22 07:00:00,2006-01-02 00:00:00,15 (christmas period 00:00-07:00) 2005-12-22 00:00:00,2006-01-02 07:00:00,25 (christmas period 07:00-00:00) The user selects dates ($from - $to) to rent a car and he gets the price accordingly. I can do a (($to-$from)/60/60) and get the total number of hours but depending on the date and time you get a different result. Can anyone help with the SQL? Thanks in advance Mario