Yes that's what I am trying to do, we currently use a local proxy server running squidnt to provide us with local filtering etc. Our ISP E2BN provides levels of filtering on different ports, middle, upper school etc. and we have squidnt configured to route user groups to the appropriate ports. Like you I have come to the conclusion it can't be done with ISA Server. Guess I will stick with SquidNT and give my brain a rest