Retreving name from customer details table

Question

i  have design customer preference screen. in that screen customer Id in dropdown list and customer name in text box.

when i click the drop down list in text box name should be displayed in customer preference screen.

i retrievethe customer id in drop down list but when click drop down name is not displayed in text box.

i customer details table id and name is there that name should come in customer preference screen.  how to do?