Checking if text within a textbox has changed

Hi i have a function which binds various data items to textboxes...
if someone changes the text within one of the text boxes before they submit on a button click i want to highlight this in a label.. can anyone help me..
eg.
====================================================================================
if textbox1.text = *has changed from its origional value*
then lbl1.text = "you have changed the text"
else
.... carry on doing whatever porcessing
end if
====================================================================================
 
Any help would be appriciated
...