website restriction in ISA server 2000

sir i want to restrict messengers msn or yahoo on client side through ISA server 2000.
thaks

The ports that you need to restrict are contained here:
http://www.chebucto.ns.ca/~rakerman/port-table.html

Yahoo Voice Chat
TCP 5000-5001 UDP 5000-5010
Services
TCP 5050 (but it will try 80 also, which makes it rather difficult to block)
Video
TCP 5100

Windows Messenger
Voice to Phone
UDP 2001-2120, 6801, 6901
File Transfers
TCP 6891-6900

For Windows Messenger in a non-UPnP environment, unfortunately Microsoft requires dynamic UDP ports across a very wide range. This is a tremendous security risk. Try to establish a UPnP environment if possible. Nevertheless, here is what they say To support [audio and video] in both directions through the firewall, all UDP ports between 5004 and 65535 must be opened to allow signaling (SIP) and media streams (RTP) to traverse the firewall.

I would advise removing Messenger by running the command line:
RunDll32 advpack.dll,LaunchINFSection %windir%\INF\msmsgs.inf,BLC.Remove

This could be placed into a login script that would remove it once a usser logs in.

You can also set a Group Policy to disallow users from adding software to a system, which would stop them in the first place.

Hope this helps.

You post a question in simplistic terms and the answer is a complex one given that ISA 2000 has many different layers of allowing or denying users public access to the internet.

Simplistically, you create a user defined protocol definition and specify port, protocol, direction, secondary connections and specify deny.