can anyone help me about this problem... im doing a reservation system.. and i have my date reserved and end date reserved... how would i know that one of my customer is near to her end date reserved...

example im CUSTOMER 1 reserved at February 18,2007 and her end date resevation is on February 24, 2007. before Feb. 24, 2007 i need to inform my customer that her reservation will be ended.. how would i know that automatically.. can anyone give me an idea...

thanks