I run my primary WOW on my main monitor as windowed + maximized (***NOT*** fullscreen), and can run additional WOWs on my 2nd LCD as 'windowed, not maximized') just fine. Win32XP, nVidia card and drivers.

It sounds like the primary wow is trying to run full-screen mode, which on some video cards will disable your secondary LCD completely.

You may also need to check your dual monitor config in windows, in mine it's set to 'dual-view', which is where each monitor acts independantly, even though I have them at the exact same resolution and refresh rate (they're identical LCDs). And I've set the second monitor to "expand my desktop onto this monitor" so I can in normal windows operation, drag windows between the two monitors simply by moving them off the edge of the screen onto the adjacent monitor.