Here is an absolutely great program that solves a pretty basic problem in an office/large network environment: How can I easily determine the IP address of my computer?
BgInfo from Sysinternals is a freeware program for Windows 95/NT4.0 and above (yes, it works on XP and Win2k). The program can be configured to display as much or as little info as you want. Literally, every little detail is there as an option. This is a must have for network administrators and a great tool to have even if you have just a little home network.
I'm using it to show the IP address of my computer on the desktop. The display and other options are completely customizable. You've got to see this one to believe it!
UPDATE 2008: Sysinternals is now owned by Microsoft.