Outlook 2003 Security Question

Ok heres the thing there's no exchage server on the network I'm refearing to and in need of a guiding hand. How can I block users from adding additional EMail account in Outlook for lets say web mail. After all you can block a site all day long but blocking it from still pulling email is a differnt animal.

Anyone have any idea. I'm half tempted to just get exchange and a book on configuring both but the cost wouldnt make it worth it for years to come.