Locking out internet excluding some sites

From: Andrew (drew_at_keyad.com)
Date: 10/31/03 

Date: Thu, 30 Oct 2003 17:06:53 -0800

I'm a NT system's administrator and I need to keep people
from entering all website's except for a select few. If
I go to Internet Options-->enable, I can choose the
websites allowed and block all others. Unfortunately, I
need to give some users the ability to go to websites
like yahoo yellowpages (http://yp.yahoo.com/) but not
allow them to check thier e-mail. When they use yellow
pages, and they try different sites, the URL is always
different. I can't put every single URL of the country
into the enable list. How can I make it to only allow
yp.yahoo.com/(all)?