I thought it was time to be a good Net citizen and run the Windows Update on my main Windows machine at home (the one with the fastest CPU, basically). Windows 2000 SP4 has been out long enough, I thought, to be stable, and so I proceeded to install that.
No problem, until I rebooted and found that my net applications (active desktop, Yahoo! Messenger, Feedreader) were all hosed. As is my habit, I dropped down to DOS and Cygwin and determined that although TCP/IP was up (I could ping on my intranet by IP), name resolution was down (nslookup and lynx would hang). I futzed around with the settings on the Local Area Connection, in the process finding that the name resolution on my wife's computer was completely out of date, but nothing helped.
Then, I noticed the "dog that did not bark." In the past, Service Pack updates would always lead to alerts from McAfee firewall that each application which was requesting access to the network had been updated since the last time such access had been granted. I was not getting any of these popups at all. So I took a closer look at the firewall settings and discovered that disabling the firewall software completely fixed DNS and NetBIOS name resolution. Even though I am behind a hardware firewall, this hardly seemed to be a good way to run, so I went to the McAfee website (the only one I've encountered which requires that I go back into IE instead of Mozilla Firebird) and reinstalled the firewall software on top of itself. After this measure and one more round of Windows Update, things appear to be back to normal
I did some searching when in the thick of things and did not found anything about SP4 breaking Firewall on 2000. So here I am on record, essentially warning the world about the "brown acid."