Is your server running the QlikView Web Server or the IIS? In any case, do the users have permissions on the folders where the QVW documents and Server files are stored? (Server files can be found in the QMC, System, Setup, QlikView Web Server, Ajax tab).
Is the Windows 2003 computer running any firewall software that is not allowing the web server port to be available to all users?
Does the server work when in the same server you use the IP instead of "localhost"?
Hope that helps.