Something which you often see Microsoft people do in their demonstrations is have the Operating System description and build number displayed on their desktop. While sysinternals do a fabulous job with their Background Info (bginfo) tool (in fact I use this myself), there is a built in facility right out the box in Windows. In the registry, navigate to HKEY_CURRENT_USER, Control Panel, Desktop, change the value of PaintDesktopVersion from 0 to 1. Logoff and back on again. Very useful when you're working with lots of virtual and test machines.
This works for Windows 2000, Windows 2003 and Windows XP, but I haven't tested NT, 9x or Me. There's also a knowledge base article available. Of course, the usual precautions about updating the registry etc., etc....
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It would be even better if computer and domain name would ALSO be shown.
You know, expecially in the scenario you mentioned with lots of VM's :-)
You can also doing this by using the Tweak UI Power Toys.