Applellial

hello, I have a textbox in my .net page, and totally new to java script. How do i get a script that will count the data being written in the text box to show increments of 100 and write the value to the bottom of the textbox. e.g. When u get to 100, at the bottom it says "1st hundred" ... and to 200 it writes "2nd hundred" UP to 500 ??? Please help thanks