From: United Kingdom
Pretty sure this applies to ISA Server 2006 too...
Configuring NLB When Joining a Server to an Array When you set up ISA Server and join the server to an existing array, ISA Server enables NLB integration for this new array member if NLB is enabled for the entire array. However, you may not want the NLB service to start automatically when installation completes, for the following reasons:
You might want to review the new array member configuration before joining it to the NLB cluster. Thereafter, you can start the NLB service on that array member.
In some cases, existing client connections may be affected when a new array member joins the NLB cluster. For this reason, you might want to schedule starting NLB on the new array member only when there is relatively little network activity.
To ensure that ISA Server does not automatically start NLB on the new array member, create a batch file, looping execution of a single command nlb suspend. Run this batch file when you install the new array member.
When NLB is configured on the new array member (after Setup completes, and while the batch file is still running), the NLB status is Suspended. To join this array member to the NLB cluster, start the NLB service, as described in Starting or Stopping a Service in this document.