Exchange and Anti-Virus

Hi. I need some suggestions on the best way to scan for viruses in an e-mail system. I have Exchange 2003. I am running Norton Anti-Virus corporate edition on the server, and have it set to scan Exchange. Clients are still getting viruses delivered to their inbox. Their NAV on their PC is catching them, luckily…but why are they even being delivered? I would like to configure the server to strip the file from the e-mail and send the e-mail through with an indication that a virus was found and stripped from the e-mail. What products can I look into? Or – maybe I have my NAV at the server configured wrong?

Thank you.