We had a pretty savvy server tech in our little 15-person office, and he had just finished setting up a new NT Server before he went to lunch. He had placed it about 2 feet to the left of an AppleShare IP server. The opportunity was too good to miss 
a) Took a screen shot of the Macintosh desktop of the AppleShare server, converted it to JPEG, and copied it across the network to the new NT Server. Took a similar screen shot of the NT Desktop and copied it to the Mac.
b) On the NT Server, moved all removable icons to a folder at the root of the C drive to get them off the Desktop. The icons that could not be removed were carefully dragged as far off-screen as possible. Then the Mac screen shot was loaded as the wallpaper.
c) On the AppleShare server, opened GraphicConverter and opened the NT screen shot, then set it for full screen mode. This served the dual function of hiding all the Mac desktop stuff and hiding the Mac menu bar at the top of the screen.
And for the coup de grâce, heh heh heh…
d) Unplugged the nice new 19" Trinitron from the new NT Server and the older 17" screen attached to the Mac and swapped them.
The screen that now sat behind the NT Server’s keyboard was cheerfully displaying the desktop that the NT Server OUGHT to be displaying, just the way he’d left it. Except it was really the Mac he was gonna be looking at, and the keyboard and mouse were still attached to the PC, so anything he did with keyboard and mouse would bring visible results on the next monitor over, which was apparently the screen of the Mac (though it was actually his NT Server).
After a couple minutes of seeing his mouse apparently frozen on screen, he does what you’d expect a PC user to do – he goes for Control-Alt-Delete to see if he can kill off some errant process that might be locking up his PC. The Mac screen over to the right obligingly pops up the NT dialog to ask if he’d like to shut down or log out or force quit something, but he isn’t looking there, and the Mac that’s actually running the screen he’s staring at decides to contribute by having its screen saver kick in right then, so he stares at the psychedelic fish swimming around on his screen in response to his Control-Alt-Delete and goes “Huh??”
We’re doubled over laughing behind his back but managing to do so silently.
He starts to reach for the power switch on the new Server’s case and we intervene: “Hey, look, I think you just force quit the Mac instead”.
He stares at what is apparently a Mac screen with the Windows dialog on it. You can almost hear the gears turning. “Now how…???”
“Could it be some kind of network interference?”, one of us asks.
“You mean like inductance or something?”, I chime in.
He moves over to sit at the Mac (the screen of which is his PC’s display) and tries to use the Mac mouse to click one of the buttons. “Hey, this computer is frozen, too”, he says, as the Mac mouse fails to move the PC mouse cursor towards the PC dialog.
He starts to get suspicious at this point because we’re snickering and grinning, but he starts tracing ethernet cables and examining the UPS and we’re doing things like “Hey Ray, the PC came back on” (moving the Mac mouse dismissed the screen saver) or “Did you check to see if the mouse got unplugged while you were back there?” (of course not, he’s just looking in the wrong place if he wants to see it moving) and he’s getting more and more bewildered. He clicks the Mac mouse again after awhile, trying to access the PC Shut Down button, and this time it de-maximizes the screen shot (on the other monitor), and I say, “Hey, this PC over here has an Apple menu now. Did you install MacOS on this Dell?” One of the other guys takes it and runs with it and confesses that HE installed the MacOS over NT on the Dell. Ray keeps staring from the Apple Menu to the tech. He tries to use the PC mouse to access the Apple Menu, no doubt wondering what the hell the menu items would be, and of course nothing moves on that screen. “But it doesn’t seem to work very well” “No, MacOS doesn’t run very well on a Dell, it keeps crashing” Poor Ray is starting to beieve it…
I dunno, maybe you had to have been there.