Capturing URL That Is TYPED Into Address Bar

My client has a training site that is associated with 4 different domains. If a user navigates away from one of the domains to another site (for instance google or msn) they want to display a message and ask them if they want meant to leave the training site. my understanding of the window.location.href is that it will not capture what is typed into the address bar until the request is submitted to the server but by then they are leaving the site. below is my code on the onbeforeunload event. concept: i want to capture the URL, compare the hostname and if the host name is one of the 4 domains then allow them to proceed if it is not then as them if they want to leave the site. if they click ok allow them to move forward, if the click cancel then reload the page. I know this is considered bad design and i have expressed this but this how they want the site to behave.

<script type="text/javascript">
function SiteCheck()
{
var strCurrentURL = window.location.href;
var strNewHostName = strCurrentURL.split("/");
//
for(i = 0; i < strNewHostName.length; i++)
{
alert(i + ' ' + strNewHostName[i]);
}
[Code]...