Users can’t access Sharepoint

I have some users on windows 2003 server who can’t display the Sharepoint web site. When they go to http://companyweb , they get “The page cannot be displayed” message.

I think these users did not authenticate to the web site when they logged in to the Domaine the first time.
How can I get them to view the site??
THank you in advance for your help.
Canaan.