When you setup your web  folder, did you the FQDN or did you use the
NetBIOS name? The security  and approval  tab will only work if you are
using the NetBIOS name because SharePoint does not allow you to
administer the workspace whether you are outside or inside the network
using the FQDN.

Well thanks for taking out some time to reply for my query. But i am
using NetBios Name when i create the web  folder.
Also have u tried it on a windows  NT 4.0 Workstation with service
pack 6a and also client  install for sps  on one machine  and got
Approvers and Security tabs working for you.

Are the clients on the same network as the SharePoint Server? This
problem will exist if they are not. I just tested it out here with an NT
box with SP6 and had no problem with the Security or the Approval tabs
when they were on the same network. I did get the problem when I was
using a PC that was on a different network and trying to connect to the
SharePoint server that was on another network.

I believe you might also have a similar problem if your server is in a DMZ.