Basically, if you are setting up a new Microsoft Internet Security and Acceleration Server with service pack 1, also known as Microsoft Forefront Threat Management Gateway, TMG. All you need to do is run this command on the first configuration storage server:
CSCRIPT KB938550.WSF /array:ISA-array-name /NLB:Muticast /Net1:name-of-the-ISA-network
KB938550.WSF is not directly available for download, but is available from Microsoft, follow the directions from KB938550
After running the script, simply setup ISA Network Load Balancing normally and it will be configured for multicast automatically.
One concern I had before I did this was how to change ISA server back to unicast from multicast. A quick look at the script explained it all as it has several examples, including:
To define NLB Unicast for a single network:
cscript kb938550.wsf /array:arrayname /nlb:unicast /net1:netname
To display the current NLB state in ISA storage:
cscript kb938550.wsf /array:arrayname /show
This week I was deploying an ISA Server 2006 with integrated NLB for a customer whose network configuration simply required the NLB to be configured for multicast. Fortunately, Microsoft continues to improve ISA server, and I was able to put this new feature to use.