Some computers cannot access OWA Exchange 2003

A few of my computers at my work place cannot access Outlook 2003 over Internet Explorer. Usually we type in webmail.*&^%$.com and we get the login screen. Instead, I’m getting “HTTP 400 – Bad Request”. Now, if I type in the actucal full name of the server, I have no problem getting to the login screen. Most of the computers do not have this issue. I think its something to do with the DNS, but I have no idea where to start. Anyone please help me out? Thank You So Much.