Well, you don't specify which webserver you are using in the first place and that is asking for not getting any workable answer.
Very generically:
* Webservers like IIS or the Windows version of Apache have limited Access Control Lists based on the Windows logon of a user. However these would not work if the server you are running on has no Windows trust with the domain in which user has logged on.
* For more advanced security and for dynamic webpages (ASP, JSP, MacroMedia etc.) a simple ACLoften is not enough. Then you need more advanced scripts. They could have their own logon mechanism or they could try to copy the workstation logon with mechanisms like Kerberos tickets (Windows Active Directory) or LDAP inquiries.
Hope this helps a bit,
- The Netherlands