AJAX :: Implement A Comment Box, Such That The Page Doesnot Reload?

i thought of a textbox and a submit button,when submit button clicked comment extracted from textbox and saved into the database using sql.and displayed in literal.but all this is server sided,please help by providing example script for the following,please note i googled and googled but cannot find a satisfy easy and efficient answerOnMouseClickextract text from textbox saving it to a variable send the variable value to server instructing it to save the value in a db in a particular field of a particular table.simple words,facebooks comment box and the status updates box how are they implemented,thousands and thousands of them use it, still it doesnot get slow no postbacks observed to page reloading etc.