disallowing access to network files

I have a win2k server and 6 workstations (5 running win2k pro and 1 winxp
pro).  The winxp pro logs into itself (not the domain).  When I wish to
access a folder on the server I get an authentication window that asks for a
username and password which I then provide.  Now I have access to all the
servers files and folders.  When I restart the computer I still have full
access.
How do I disallow this priveledge so the window pops up again asking for my
username and password.  Ideally I'd like for the workstation to just be able
to access 1 folder on the server and that is it!

You currently have an account/password on the server that matches

You currently have an account/password on the server that matches the
account/password on your workstations. When you delete the server account
then you will be challenged each time you log on.