Jan 21, 2008 12:57 PM|dhanabalanr|LINK
You need to call dropdownlist selected index changed event, in that fetch data from releated table and assign them to the text boxes.
If you are using ajax then you have to put all controls inside the updatepanel except and dropdown list and you can set the async postback trigger
as dropdownlist selected index changed event
otherwise you can use icallback