If you don't want to drill, but have (and can use) a pair of "Wire" or "Side' cutters, you can usually cut out the stamped grill guards over the case fans and replace them with the chrome round fan guards. Airflow can increase tremendously from using these guards vs the stamped guards...which tend to build up backpressure and not let the air flow freely into/out of the case.
Then there's...faster fans....or FAST fans with thermal control...i.e. If the case gets hotter, the fans speed up. Other ideas are to replace the IDE cables (assuming they are ribbon) with the ROUND IDE cables to let air flow better in the case.
I will say this...I sometimes don't think the case temperature sensor is always accurate...as I've got two K7AMA boards that have a 46C full load CPU reading...while keeping a 41C case temp...which I know is not true! I can blow a full size fan on the board with open side panel and only lower it to 39C! :Q