how to create text box dynamically in asp.net,c#

Hi
I have aspx page  in that i have dropdownlist .
i got dropdownlist values 'Ram'  35
'alex' 40
'krish'  28
'others' 30
if i click 'others' a new text box will be created and only one instance
if i click other names that textbox will be removed.
 
I want to do in javascript to avoid post back.
I want to save that textbox value in severside.
please help me to get solution
Thanks
chandran
<div> </div>