SharePoint authentication problem

Dear Everyone,

I am running Sharepoint 2007(Single server, server farm) on SQL 2005 with Windows 2003 server, however, I got a strange authentication problem.

The server name is called sharepoint01, however, I am unable to connect to it using URLhttp://sharepoint01 and always return with 401 authentication error page after prompting for credential 3 times, instead there is another host record on DNS server and pointed to the name intranet with the same IP address.  When connecting using URL http://intranet, it works with "windows authentication" without even asking for user credential. 

I tried to create another host record on DNS using another name, intranet01, the URLhttp://intranet01 works as well using "windows authentication". 

Why the default server name does not work?  The sharepoint01, intranet and intranet01 are not added to the trusted zone on IE.

Thanks