Passing authentication for windows 2000

I am using Exchange 2000 OWA on Windows 2000. I need to be able to pass NT credentials to the server for our sales dept. to get to their mailboxes via OWA, but I want to elimate the sign on box that pops up when they get to the page. Is there any way that I can pass their username and password that would keep the box from popping up, without having to turn anonymous on?