I very much doubt it using only script. If you have control of the browser, a company intranet for example you might be able to use Group Policy, if that fails then a browser helper object would be needed which would need to be installed. There are also many other ways to get the URL of a page. You can only disable the title bar if the site is in the trusted sites security zone or local intranet.
In my opinion if it's that important to stop users knowing the URL you shouldn't be using a browser-based application.
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Joe (
Microsoft MVP - XML)