Modifying The Look / Function Of An Alert Box

<script type="text/javascript">
function confirmation()
{
alert(
"Please Confirm Before Proceeding !" +
"
" +
"Display Name: " + document.forms["paypal"]["os0"].value +
[Code]....

First though JS is not my strong suit and the above code is something I found at the W3School site or whatever it is. What I would like to do if possible is add a Cancel button to the alert box that when clicked cancels the form submission it's attached to and keeps the user on the current page to modify the data they entered in to the form should they want to change it. As it stands, all there is is an Ok button and if you click the red x in the corner it acts as if you clicked ok so if a user wanted to change their form data they'd have to close the browser to start again. Aside from liking to add a cancel button I would also like to if possible change the alerts Ok button to read something different. Not sure yet, thinking either Submit or Proceed.