I have written this post on ISA/TMG product website. Its about NLB (unicast) on a VMware(virtual setup) machine.

Here is the link

http://blogs.technet.com/b/isablog/archive/2010/11/04/unable-to-fail-over-from-one-tmg-node-to-another-when-using-nlb-in-a-virtual-environment.aspx?wa=wsignin1.0