How to process string in Textbox   

Hi ! Can you tell me How to create a string flowing :
1. Create a Textbox
2. I want , When I type into Textbox in TextChange Events:
 ex : 1234567 then It must display as 1,234,567 or 1.234.567.
Help Me !
Contact : hoangnhan_schoolnet@yahoo.com

date: Thu, 31 Mar 2005 20:35:01 -0800   author:   Mr Nhan Mr