I recall a problem with Win2K losing the first DNS server, and falling back on the secondary. This drove us nuts for quite a while at work, since desktops would stop resolving stuff on the local net, but could resolve names in the outside world. I *think* that we resolved the problem by adding a second internal DNS server, so that losing the first was benign. At the time (~3 year back) there was chatter on the net about the problem, but no acknowledgement from Microsoft.

The DNS server happened to also be Win2K, though that appeared to be unrelated to the client problem.