dropdown confirm message box

[hamsinii]

On selected index changed of the dropdown list, I want a confirm message box informing the user few details. Based on the user acceptance, I need to continue executing the server side code written for dropdown_selectedIndexChanged event. Now, if I place the javascript function for the confirm message box in the html part, it does not trigger the server side event. If it does trigger the server side event , the javascript doesnt trigger. How do I get it to execute both, the client side javascript as well as the server side event handler.