ActionScript 2.0 :: How To Implement Chat Textfield

i want to implement chating textbox. if 1 user types in input text and press buton that text should come in textfield.again if other user enters sumthing it should come next like that. i placed folowing code in buton press.

Code:
on (press) {
chat_txt.replaceText(0,chat_txt.length,chat_txt.text+input_txt.text);
input_txt.text=""
}

here it is adding wht i entered second in the first line but i want it on the second line.How can do that?