dropdown list using ajax

i have a dropdownlist in which countrynames are binded from sql server data table.now i want that when i select a country name then another dropdown list appear with the statenames according to the selected country name. i have made two tables for this,one containing countryid and states and another containg stateid with their respective countryid and state names.i read the cascading dropdownlist but in that two dropdownlists are taken in the form.how can i do this using AJAX without doing postback.kindly help me.