One of the greatest challenges in configuring the ISA firewall is getting NLB to work properly when configuring it to work with the Enterprise edition of the firewall. Sure, the ISA dev team did a great job at integrating NLB functionality into the firewall's interface, and for that we are grateful. However, NLB has dependencies outside the firewall configuration itself. NLB has to work with other components of the network infrastructure. In addition, there are two different implementations of NLB -- unicast and multicast.
While there are good resources spread across a number of sites in how to get NLB to work, there hasn't been a "one stop shop" where you could go to get all the links and information you need to help setup and troubleshoot your NLB setups. Well, those days are over. Jason Jones has put together an ISA NLB resource site that has everything you need to get your NLB up and running.
That isn't to say that it's going to be easy. First you need to wrap your head around NLB concepts, and then you're going to need to understand how the switches in your environment work. You might even need to reconfigure your switching infrastructure.
For Jason's NLB resource center, check out:
Thomas W Shinder, M.D., MCSE
Sr. Consultant / Technical Writer