As mentioned above, due to Integrated Authentication support configured on ISA server, third party browsers do not work behind it. In this situation you can make use of another authentication scheme called 'Basic Authentication', commonly supported by most browsers and most importantly by ISA Server too. If you work in a security conscious environment this method is not recommended since during basic authentication, the username and password sent are loosely encrypted.
The point here is that to proceed with this method you will have to make sure that you have legitimate access over configuring the ISA Server. If you cannot access the server configuration console, then move on to the second method in the following section.
All you need to do is fire up 'ISA Management' and follow these steps:
In particular, we will take Netscape as an example here.
Load up a test url in your browser, it will ask you for authentication information, In place of user, type DOMAIN\USER, where your DOMAIN being the Windows domain, and USER being a legitimate domain user. In place of password, type the user's password. Click on OK to continue. For example:
User: CABLENET\Raheel Password: Mypassword Where CABLENET is my domain, Raheel is the user id and Mypassword is my password.
You should now see the page loading successfully. If you use a different browser you will need to explore and see if it supports Basic Authentication.